[Infra] Use Xcode 16.4 in spm.yml

Author: ncooke3

.github/workflows/spm.yml

@@ -11,6 +11,8 @@ jobs:
     runs-on: macOS-latest
     steps:
     - uses: actions/checkout@v2
+    - name: Set Xcode version
+      run: sudo xcode-select -s /Applications/Xcode_16.4.app
     - name: Initialize xcodebuild
       run: xcodebuild -list
     - name: iOS Simulator Build Tests