arm64 runner on CI

Author: hannesa2

.github/workflows/BuildPR.yml

@@ -5,11 +5,17 @@ on: [ pull_request ]
 jobs:
   build-objective-git:
     name: Build objective-git
-    runs-on: macOS-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
+        os: [ macos-11 ]
+        abi: [ x86_64 ]
         xcode: [ Xcode_12.4, Xcode_13.2.1 ]
+        include:
+          - xcode: Xcode
+            os: ARM64
+            abi: arm64
     steps:
       - name: ls Xcode
         run: ls -la /Applications/Xcode*
@@ -23,4 +29,4 @@ jobs:
       - name: pre build
         run: script/bootstrap && script/update_libgit2
       - name: Test and archive project
-        run: xcodebuild -workspace ObjectiveGitFramework.xcworkspace -scheme "ObjectiveGit Mac" test archive ARCHS="x86_64"
+        run: xcodebuild -workspace ObjectiveGitFramework.xcworkspace -scheme "ObjectiveGit Mac" test archive ARCHS="${{ matrix.abi }}"