CI(pre-merge-checks): run on PRs... sometimes...

.github/workflows/pre-merge-checks.yml

@@ -4,6 +4,13 @@ on:
   merge_group:
     branches:
       - main
+  # Trigger the workflow also on PRs which changes the workflow itself or reusable workflow it uses.
+  # Note, that `conclusion` job will be skipped for such PRs.
+  pull_request:
+    paths:
+      - '.github/workflows/pre-merge-checks.yml'
+      - '.github/workflows/build-build-tools-image.yml'
+      - '.github/workflows/_check-codestyle-python.yml'
 
 defaults:
   run:
@@ -35,7 +42,7 @@ jobs:
           echo "${PYTHON_CHANGED_FILES}"
 
   build-build-tools-image:
-    if: needs.get-changed-files.outputs.python-changed == 'true'
+    if: needs.get-changed-files.outputs.python-changed == 'true' || github.event_name == 'pull_request'
     needs: [ get-changed-files ]
     uses: ./.github/workflows/build-build-tools-image.yml
     with:
@@ -45,7 +52,7 @@ jobs:
     secrets: inherit
 
   check-codestyle-python:
-    if: needs.get-changed-files.outputs.python-changed == 'true'
+    if: needs.get-changed-files.outputs.python-changed == 'true' || github.event_name == 'pull_request'
     needs: [ get-changed-files, build-build-tools-image ]
     uses: ./.github/workflows/_check-codestyle-python.yml
     with:
@@ -58,7 +65,7 @@ jobs:
   # - conclusion
   # - neon-cloud-e2e
   conclusion:
-    if: always()
+    if: always() && github.event_name != 'pull_request'
     permissions:
       statuses: write # for `github.repos.createCommitStatus(...)`
     needs: