ci(verify-make-gen): limit push trigger to master (#8069)

Currently triggered on any branch push in the repo.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

.github/workflows/verify-make-gen.yml

@@ -1,5 +1,9 @@
 name: Verify Generated Files
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
 permissions:
   contents: read