[CI] tests fail to build on macOS ARM64 runner

[zacharyburnett]

The cmake --build . --parallel step takes 30 minutes and then is cancelled:

[ 66%] Building CXX object CMakeFiles/s2shapeutil_build_polygon_boundaries_test.dir/src/s2/s2shapeutil_build_polygon_boundaries_test.cc.o
[ 66%] Building CXX object CMakeFiles/value_lexicon_test.dir/src/s2/value_lexicon_test.cc.o
Error: The operation was canceled.

https://github.com/google/s2geometry/actions/runs/13096798651/job/36540005166#step:7:264

The same step takes ~3 minutes on macOS x64 and ~8 minutes on Ubuntu x64

[zacharyburnett]

I'm not sure what is different about the ARM64 environment that specifically causes the build to be so slow. As far as I understand, the GitHub-provided ARM64 runner has 3 cores available yet takes 10 times as long as the x64 one which has 2. Perhaps the cmake --parallel is causing issues?