Run slow macOS checks on larger runners

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

pr-checks/checks/all-platform-bundle.yml

@@ -2,7 +2,8 @@ name: "All-platform bundle"
 description: "Tests using an all-platform CodeQL Bundle"
 operatingSystems:
   - ubuntu
-  - macos
+  - os: macos
+    runner-image: macos-latest-xlarge
   - windows
 versions:
   - nightly-latest

pr-checks/checks/swift-custom-build.yml

@@ -5,7 +5,8 @@ versions:
   - default
   - nightly-latest
 operatingSystems:
-  - macos
+  - os: macos
+    runner-image: macos-latest-xlarge
 installGo: true
 installDotNet: true
 env: