ENH: Add notebook run GitHub Actions workflow file

Add notebook run GitHub Actions workflow file, and the accompanying
headless setup shell script.

Left behind by the Carpentries Workbench infrastructure automated
transition tool in commits 560b5b4, and 6dab472.

.github/scripts/setup_headless.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+echo "DISPLAY=:99.0" >> $GITHUB_ENV
+
+if [ "$RUNNER_OS" == "Linux" ]; then
+    echo "LIBGL_ALWAYS_SOFTWARE=1" >> $GITHUB_ENV
+    echo "LIBGL_ALWAYS_INDIRECT=0" >> $GITHUB_ENV
+    sudo apt-get install -y libgl1-mesa-glx xvfb
+    Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
+    sleep 3
+elif [ "$RUNNER_OS" == "Windows" ]; then
+    powershell ./tools/ci/install_opengl.ps1
+elif [ "$RUNNER_OS" == "macOS" ]; then
+    echo 'Install Xquartz package for headless'
+    brew install --cask xquartz
+fi
+

.github/workflows/build-test.yaml

@@ -0,0 +1,135 @@
+name: Build, test
+
+on:
+  push:
+    branches: ['main']
+  pull_request:
+
+# Allow a subsequently queued workflow run to interrupt previous runs
+concurrency:
+  group: '${{ github.workflow }}-${{ github.event.pull_request.head.label || github.head_ref || github.ref }}'
+  cancel-in-progress: true
+
+jobs:
+  build:
+    if: "!contains(github.event.head_commit.message, '[skip ci]')"
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ['3.8', '3.9', '3.10', '3.11']
+    env:
+      ANTSPATH: /opt/ants
+      FSLPATH: /opt/fsl
+      FSLDIR: /opt/fsl
+      FSLOUTPUTTYPE: NIFTI_GZ
+      FSLVERSION: 6.0.6.5
+
+    steps:
+    - name: Cache Ubuntu dependencies
+      uses: actions/cache@v3
+      with:
+        path: |
+          /var/lib/apt
+          !/var/lib/apt/lists/partial
+          !/var/lib/apt/lists/lock
+        key: apt-cache-v1
+        restore-keys: |
+          apt-cache-v1
+
+    - name: Install Ubuntu dependencies
+      run: |
+        sudo apt-get update
+        sudo apt-get install -y --no-install-recommends \
+                             bc \
+                             bzip2 \
+                             ca-certificates \
+                             curl \
+                             dc \
+                             file \
+                             libfontconfig1 \
+                             libfreetype6 \
+                             libgl1-mesa-dev \
+                             libgl1-mesa-dri \
+                             libglu1-mesa-dev \
+                             libgomp1 \
+                             libice6 \
+                             libxcursor1 \
+                             libxft2 \
+                             libxinerama1 \
+                             libxrandr2 \
+                             libxrender1 \
+                             libxt6
+        sudo apt-get clean
+
+    - name: Cache ANTs install
+      uses: actions/cache@v3
+      with:
+        path: /opt/ants
+        key: ants-v1
+        restore-keys: |
+          ants-v1
+
+    - name: Install ANTs
+      run: |
+        if [[ ! -d "${ANTSPATH}" ]]; then
+          sudo mkdir -p $ANTSPATH
+          curl -sSL "https://dl.dropbox.com/s/gwf51ykkk5bifyj/ants-Linux-centos6_x86_64-v2.3.4.tar.gz" | sudo tar -xzC $ANTSPATH --strip-components 1
+        fi
+
+    - name: Cache FSL install
+      uses: actions/cache@v3
+      with:
+        path: $FSLPATH
+        key: fsl-v2
+        restore-keys: |
+          fsl-v2
+
+    # Run with multiple Python versions
+    - name: Setup Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v4
+      with:
+        python-version: ${{ matrix.python-version }}
+
+    - name: Install FSL
+      run: |
+        if [[ ! -d "${FSLPATH}" ]]; then
+          sudo mkdir -p $FSLPATH
+          curl https://fsl.fmrib.ox.ac.uk/fsldownloads/fslconda/releases/fslinstaller.py -o /tmp/fslinstaller.py -s
+          python /tmp/fslinstaller.py -d ${FSLPATH} -V ${FSLVERSION} -o
+          sudo rm -rf ${FSLPATH}/data/atlases
+          rm /tmp/fslinstaller.py
+        fi
+
+    - name: Checkout GitHub repository
+      uses: actions/checkout@v3
+
+    - name: Install dependencies for headless display
+      run: |
+        ${{ github.workspace }}/.github/scripts/setup_headless.sh
+
+    - name: Install Python requirements
+      if: steps.cache.outputs.cache-hit != 'true'
+      run: |
+        python -m pip install --upgrade pip
+        pip install -r requirements.txt
+        pip install pytest nbval
+
+    - name: Download data
+      run: |
+        pushd `pwd`
+        cd ${{ github.workspace }}/data
+        osf -p cmq8a fetch ds000221_subject/ds000221_sub-010006.zip
+        unzip ds000221_sub-010006.zip
+        rm ds000221_sub-010006.zip
+        popd
+
+    - name: Run pytest on Jupyter notebooks
+      run: |
+        export PYTHONPATH=$PYTHONPATH:`realpath ${{ github.workspace }}`
+        export PATH=$FSLPATH/bin:$ANTSPATH:$PATH
+        pytest --nbval-lax -v code/introduction.ipynb
+        pytest --nbval-lax -v code/preprocessing.ipynb
+        pytest --nbval-lax -v code/diffusion_tensor_imaging.ipynb
+        pytest --nbval-lax -v code/constrained_spherical_deconvolution.ipynb
+        pytest --nbval-lax -v code/deterministic_tractography.ipynb
+        pytest --nbval-lax -v code/probabilistic_tractography.ipynb