Use Xcode 13.0 in GitHub Actions workflows

Author: MaxDesiatov

.github/workflows/build-toolchain.yml

@@ -17,7 +17,7 @@ jobs:
   build_toolchain:
     env:
       TOOLCHAIN_CHANNEL: DEVELOPMENT
-      DEVELOPER_DIR: /Applications/Xcode_12.5.app/Contents/Developer/
+      DEVELOPER_DIR: /Applications/Xcode_13.0.app/Contents/Developer/
     strategy:
       matrix:
         include: