Update main.yml to use GCC 12 as 11 is no longer available on macos i…

…mage

[[macOS] GCC 11 will be removed from all macOS images on August 12](actions/runner-images#10213)

.github/workflows/main.yml

@@ -418,8 +418,8 @@ jobs:
         # https://github.com/actions/runner-images/issues/6350
         sudo xcode-select -s '/Applications/Xcode_13.4.1.app/Contents/Developer'
         
-        echo 'CC=gcc-11' >> $GITHUB_ENV
-        echo 'CXX=g++-11' >> $GITHUB_ENV
+        echo 'CC=gcc-12' >> $GITHUB_ENV
+        echo 'CXX=g++-12' >> $GITHUB_ENV
         echo "PATH=$(brew --prefix)/opt/ccache/libexec:$PATH" >> $GITHUB_ENV
         echo 'PREFIX=${GITHUB_WORKSPACE}/install' >> $GITHUB_ENV
         echo "$PREFIX" >> $GITHUB_PATH