ci: fix pr file checker (#9694)

* filter github pr file checker on the right labels object

* only check PR files when the PR is opened

.github/workflows/pr-file-checker.yml

@@ -7,8 +7,8 @@
 # never call any makefiles or scripts. It must never be changed to run any code from the checkout.
 on:
   pull_request_target:
+    types: [opened]
     # Runs on PRs to master and all release branches
-    # By default it triggers on opened, synchronize, or reopened PRs
     branches:
       - master
       - release/*
@@ -17,7 +17,7 @@ jobs:
   # checks that a .changelog entry is present for a PR
   changelog-check:
     # If there  a `pr/no-changelog` label we ignore this check
-    if: "!${{ contains(github.event.pull_request.label.*.name, 'pr/no-changelog')}}"
+    if: "!${{ contains(github.event.pull_request.labels.*.name, 'pr/no-changelog')}}"
     runs-on: ubuntu-latest
 
     steps:
@@ -46,7 +46,7 @@ jobs:
   # checks that a 'type/docs-cherrypick' label is attached to PRs with website/ changes
   website-check:
     # If there's a `type/docs-cherrypick` label we ignore this check
-    if: "!${{ contains(github.event.pull_request.label.*.name, 'type/docs-cherrypick')}}"
+    if: "!${{ contains(github.event.pull_request.labels.*.name, 'type/docs-cherrypick')}}"
     runs-on: ubuntu-latest
 
     steps: