Use latest stable xcode

Author: Deadpikle

.github/workflows/main.yml

@@ -22,6 +22,9 @@ jobs:
     runs-on: macos-latest
     steps:
     - uses: actions/checkout@v2
+    - uses: maxim-lobanov/[email protected]
+      with:
+        xcode-version: latest-stable
     - run: bash boost.sh
     - name: Upload built boost.xcframework
       uses: actions/upload-artifact@v2