visionOS buildonly on macos-13

Author: paulb777

.github/workflows/abtesting.yml

@@ -72,6 +72,11 @@ jobs:
         target: [iOS, tvOS, macOS, catalyst, watchOS]
         os: [macos-14]
         xcode: [Xcode_15.2, Xcode_16]
+        include:
+          - os: macos-13
+            xcode: Xcode_15.2
+            target: visionOS
+            spmbuildonly: buildonly
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v4
@@ -89,7 +94,7 @@ jobs:
         max_attempts: 3
         retry_on: error
         retry_wait_seconds: 120
-        command: scripts/build.sh ABTestingUnit ${{ matrix.target }} spm
+        command: scripts/build.sh ABTestingUnit ${{ matrix.target }} spm${{ matrix.buildonly }} 
 
   catalyst:
     # Don't run on private repo unless it is a PR.