Add "opened" to triggers for version check

We've had a few instances, where the PR target branch
mismatched the WP version, but it was only noticed after
a second push to the pull request (presumably that's the
"synchronize" type).

This change intends to ensure that the version check is already
performed, when the PR is opened.

Author: NobodysNightmare

.github/workflows/version-check.yml

@@ -2,7 +2,11 @@ name: Check work package version
 
 on:
   pull_request:
-    types: [labeled, synchronize, ready_for_review]
+    types:
+      - opened
+      - labeled
+      - synchronize
+      - ready_for_review
 
 permissions:
   contents: read # to fetch code (actions/checkout)