fix: remove pull_request trigger to avoid frequent runs

Only trigger on:
- Release (prereleased/released)
- Push to main (after PR merge)
- Manual dispatch

Author: kaisongli

.github/workflows/oc2ov_test.yml

@@ -6,10 +6,6 @@ on:
   push:
     branches:
       - main
-  pull_request:
-    branches:
-      - main
-    types: [opened, synchronize, reopened]
   workflow_dispatch:
     inputs:
       skip_tests: