CI: macOS w/ -Werror Again

Add `-Werror` back to macOS CI.
Was temporarily disabled until
AMReX-Codes/pyamrex#453
landed in ImpactX.

Author: ax3l

.github/workflows/macos.yml

@@ -63,6 +63,8 @@ jobs:
         export CCACHE_SLOPPINESS=time_macros
         ccache -z
 
+        export CXXFLAGS="-Werror -Wno-error=pass-failed"
+
         cmake -S . -B build            \
           -DCMAKE_VERBOSE_MAKEFILE=ON  \
           -DImpactX_FFT=ON             \