lock xcode to 16.4

Author: iSapozhnik

.github/workflows/pr-tests.yml

@@ -42,7 +42,7 @@ jobs:
       - name: Select latest stable Xcode
         uses: maxim-lobanov/setup-xcode@v1
         with:
-          xcode-version: "latest-stable"
+          xcode-version: "16.4"
 
       - name: Install xcsift
         run: brew install xcsift