Only attempt to install pods when linting strings if CP is found

As we start removing CocoaPods from some of our projects, we can no
longer assume pods exist locally to install.

See wordpress-mobile/WordPress-iOS#23951 which
prompted this change.

bin/lint_localized_strings_format

@@ -13,7 +13,11 @@ install_gems
 # The strings generation also picks up files from our first party libraries,
 # some of which are installed via CocoaPods
 echo "--- :cocoapods: Setting up Pods"
-install_cocoapods
+if [[ -f Podfile.lock ]]; then
+  install_cocoapods
+else
+  echo "CocoaPods setup not detected. Skipping CocoaPods installation..."
+fi
 
 echo "--- :sleuth_or_spy: Lint Apple Localized Strings Format"
 # A next step improvement is to move the logs management within the release