CI: change use of FORCE_JULIAINTERFACE_COMPILATION

[fingolfin]

I might be mistaken on the following (and am running this in CI to test it). But:

So far we set FORCE_JULIAINTERFACE_COMPILATION in one invocation of gap.sh; but then omitted it for the next couple. But then those other runs will use the stock version from the JLL again, defeating the whole point of forcing recompilation with --coverage enabled.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.46%. Comparing base (5f9a8d6) to head (b3d85f2).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1339       +/-   ##
===========================================
- Coverage   80.90%   70.46%   -10.45%     
===========================================
  Files          61       45       -16     
  Lines        4903     3081     -1822     
  Branches        0       31       +31     
===========================================
- Hits         3967     2171     -1796     
+ Misses        936      910       -26     

see 30 files with indirect coverage changes

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[fingolfin]

Huh, this now fails on macOS when linking against GAP built from sources (but only with Julia 1... wtf

ERROR: LoadError: InitError: could not load library "/var/folders/yz/zr09txvs5dn18vt4cn21kzl40000gn/T/jl_jjifc6/artifacts/ee3616e1fde171bed644306185339257da9171fe/lib/gap/JuliaInterface.so"
dlopen(/var/folders/yz/zr09txvs5dn18vt4cn21kzl40000gn/T/jl_jjifc6/artifacts/ee3616e1fde171bed644306185339257da9171fe/lib/gap/JuliaInterface.so, 0x0001): Library not loaded: @rpath/libgap.10.dylib
  Referenced from: <4C4C440E-5555-3144-A15F-C2466FC3FF28> /private/var/folders/yz/zr09txvs5dn18vt4cn21kzl40000gn/T/jl_jjifc6/artifacts/ee3616e1fde171bed644306185339257da9171fe/lib/gap/JuliaInterface.so
  Reason: tried: '/private/var/folders/yz/zr09txvs5dn18vt4cn21kzl40000gn/T/jl_jjifc6/artifacts/ee3616e1fde171bed644306185339257da9171fe/lib/gap/../libgap.10.dylib' (no such file), '/private/var/folders/yz/zr09txvs5dn18vt4cn21kzl40000gn/T/jl_jjifc6/artifacts/ee3616e1fde171bed644306185339257da9171fe/lib/gap/../libgap.10.dylib' (no such file), '/Users/runner/hostedtoolcache/julia/1.12.4/aarch64/lib/julia/libgap.10.dylib' (no such file), '/Users/runner/hostedtoolcache/julia/1.12.4/aarch64/lib/julia/../libgap.10.dylib' (no such file), '/Users/runner/hostedtoolcache/julia/1.12.4/aarch64/lib/libgap.10.dylib' (no such file), '/usr/local/lib/libgap.10.dylib' (no such file), '/usr/lib/libgap.10.dylib' (no such file, not in dyld cache)