Add Xcode setup step with latest stable version in pull_request.yml

Author: Reedyuk

.github/workflows/pull_request.yml

@@ -128,6 +128,9 @@ jobs:
             */build/cocoapods
             */build/classes
           key: cocoapods-cache-v2
+      - uses: maxim-lobanov/setup-xcode@v1
+        with:
+          xcode-version: latest-stable
       - name: Setup test environment
         uses: ./.github/actions/setup_test_action
       - name: Set Artifact Name