Merge pull request #1538 from albinahlback/fix_flint_version #1112

Job	Run time
Ubuntu Clang (x1)	2m 43s
Cygwin GCC (x0.5)	2m 19s
macOS GCC with BLAS (x1)	2m 30s
FreeBSD Clang (x0.5)	2m 25s
Ubuntu GCC via CMake (no check)	2m 44s
Ubuntu GCC, default flags with AVX2, Code Coverage (x3)	2m 55s
Ubuntu GCC (assert, x1)	2m 40s
MinGW GCC (x0.5)	2m 21s
MSVC (x1, excl test)	2m 21s
Nemo.jl	2m 39s
	25m 37s

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