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 65.53%. Comparing base (3eb636d) to head (ac5745e).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1339       +/-   ##
===========================================
- Coverage   78.03%   65.53%   -12.51%     
===========================================
  Files          61       44       -17     
  Lines        4945     3029     -1916     
===========================================
- Hits         3859     1985     -1874     
+ Misses       1086     1044       -42     

see 27 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)