Rename action to check msgid changes (#1365)

The focus of the action is to check and validate changes to the `msgid`
fields, not to totally prevent such changes.

This also makes the `paths` a little more precise: we only care about
changes to `po/*.po`.

.github/workflows/check-msgid-changes.yml

@@ -0,0 +1,21 @@
+name: Prevent unintended msgid changes
+
+on:
+  pull_request:
+    paths:
+      - "po/*.po"
+
+jobs:
+  check-msgid-changes:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Reset git
+        run: git reset origin/main
+
+      - name: Check po file changes
+        run: python3 .github/workflows/check-msgid-changes.py