Bump stable branch version after release.

* configure.ac (AC_INIT): Set version to 9.3.1.
(OCTAVE_PATCH_VERSION): Now 1.
* NEWS.9.md: Create section for a future 9.4 release.

configure.ac

@@ -27,7 +27,7 @@ dnl
 
 ### Initialize Autoconf
 AC_PREREQ([2.65])
-AC_INIT([GNU Octave], [9.3.0], [https://octave.org/bugs.html], [octave],
+AC_INIT([GNU Octave], [9.3.1], [https://octave.org/bugs.html], [octave],
         [https://www.gnu.org/software/octave/])
 
 ### Declare version numbers
@@ -41,7 +41,7 @@ dnl AC_INIT requires it to be static, not computed from shell variables.
 
 OCTAVE_MAJOR_VERSION=9
 OCTAVE_MINOR_VERSION=3
-OCTAVE_PATCH_VERSION=0
+OCTAVE_PATCH_VERSION=1
 
 dnl PACKAGE_VERSION is set by the AC_INIT VERSION argument.
 OCTAVE_VERSION="$PACKAGE_VERSION"

etc/NEWS.9.md

@@ -1,5 +1,17 @@
 For (bug #XXXXX) see https://savannah.gnu.org/bugs/?XXXXX
 
+Summary of bugs fixed for version 9.4.0 (tbd):
+-----------------------------------------------------
+
+### Improvements and fixes
+
+### GUI
+
+### Build system / Tests
+
+### Documentation
+
+
 Summary of bugs fixed for version 9.3.0 (2024-12-12):
 -----------------------------------------------------