restore hermetic generation workflow

Author: diegomarquezp

.github/workflows/hermetic_library_generation.yaml

@@ -15,8 +15,7 @@
 # downstream client libraries before they are released.
 name: Hermetic library generation upon generation config change through pull requests
 on:
-  # TODO: uncomment this before merging to prevent a formatting regression
-  #pull_request:
+  pull_request:
   workflow_dispatch:
 
 env: