Cancel current CI actions when a PR is updated

This should help get build feedback more quickly when someone is iterating on a PR

.github/workflows/ios.yml

@@ -2,6 +2,10 @@ name: Build (iOS/tvOS)
 
 on: [push, pull_request]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   Build:
     name: ${{ matrix.platform.name }}
@@ -17,4 +21,4 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Build
-        run: xcodebuild -project Xcode/SDL/SDL.xcodeproj -target '${{ matrix.platform.target }}' -configuration Release -sdk ${{ matrix.platform.sdk }} clean build
+        run: xcodebuild -project Xcode/SDL/SDL.xcodeproj -target '${{ matrix.platform.target }}' -configuration Release -sdk ${{ matrix.platform.sdk }} clean build