ci: brew prefix

On intel macOS, brew installs into /usr/local
On apple silicon, brew installs into /opt/homebrew

Use brew --prefix to resolve the right brew prefix in a platform independent manor

.github/actions/ngen-build/action.yaml

@@ -82,11 +82,11 @@ runs:
             elif [ ${{ runner.os }} == 'macOS' ]
             then
               brew install netcdf netcdf-cxx netcdf-fortran
-              echo "LIBRARY_PATH=/usr/local/lib/:$LIBRARY_PATH" >> $GITHUB_ENV
-              echo "LD_LIBRARY_PATH=/usr/local/lib/:$LD_LIBRARY_PATH" >> $GITHUB_ENV
-              echo "LDFLAGS=-L/usr/local/lib" >> $GITHUB_ENV
+              echo "LIBRARY_PATH=$(brew --prefix)/lib/:$LIBRARY_PATH" >> $GITHUB_ENV
+              echo "LD_LIBRARY_PATH=$(brew --prefix)/lib/:$LD_LIBRARY_PATH" >> $GITHUB_ENV
+              echo "LDFLAGS=-L$(brew --prefix)/lib" >> $GITHUB_ENV
               echo "LIB=$LD_LIBRARY_PATH" >> $GITHUB_ENV
-              echo "NETCDF=/usr/local" >> $GITHUB_ENV
+              echo "NETCDF=$(brew --prefix)" >> $GITHUB_ENV
             fi
           shell: bash