Add new GH Action for ensuring the correct labels are added to PRs (#…

…10412)

* Add new GH Action for ensuring the correct labels are added to PRs.

* Update Pull Request Template instructions for labels.

* Update validation.

* Update the validation for the type.

.github/pull_request_template.md

@@ -18,6 +18,7 @@ Fixes #
 
 #### Other Checks
 
+- [ ] This PR has either a `[type]` label or a `[skip-changelog]` label.
 - [ ] This PR adds/removes a feature flag & I've updated [this doc](https://github.com/woocommerce/woocommerce-blocks/blob/trunk/docs/internal-developers/blocks/feature-flags-and-experimental-interfaces.md).
 - [ ] This PR adds/removes an experimental interfaces and I've updated [this doc](https://github.com/woocommerce/woocommerce-blocks/blob/trunk/docs/internal-developers/blocks/feature-flags-and-experimental-interfaces.md).
 - [ ] I tagged two reviewers because this PR makes queries to the database or I think it might have some security impact.

.github/workflows/pr-label-validation.yml

@@ -0,0 +1,24 @@
+name: Pull Request Label Validation
+
+on:
+  pull_request:
+    branches:
+      - trunk
+    types:
+      - labeled
+      - unlabeled
+      - opened
+      - reopened
+      - synchronize
+      - edited
+
+env:
+  LABELS: ${{ join( github.event.pull_request.labels.*.name, ' ' ) }}
+
+jobs:
+  check-type-label:
+    name: Check [Type] Label
+    runs-on: ubuntu-latest
+    steps:
+      - if: contains( env.LABELS, 'type' ) == false && contains( env.LABELS, 'skip-changelog' ) == false
+        run: exit 1