ci: Fix Validate podspec (#2253)

Since October 3rd the default Xcode version is 14.0.1,
which breaks pod lib lint. Ideally, we fix the underlying issue
but for now, let's keep using Xcode 13.4.1 for pod lib lint.

.github/workflows/lint.yml

@@ -45,6 +45,7 @@ jobs:
     runs-on: macos-12
     steps:
       - uses: actions/checkout@v3
+      - run: ./scripts/ci-select-xcode.sh
       - name: Validate Podspec
         run: pod lib lint --verbose
         shell: sh