Remove milestone from unmerged PRs (woocommerce#41216)

* Remove milestone from unmerged PRs

* Add pr write permission to milestone manager

.github/workflows/milestoned.yml

@@ -0,0 +1,26 @@
+name: Milestone Manager
+
+on:
+    pull_request_target:
+        types: [milestoned]
+
+permissions: {}
+
+jobs:
+    remove-milestone-from-unmerged-prs:
+        name: "Remove Milestone from Unmerged PRs"
+        if: github.event.pull_request.merged != true
+        runs-on: ubuntu-latest
+        permissions:
+            issues: write
+            pull-requests: write
+        steps:
+            - uses: actions/github-script@v6
+              with:
+                  script: |
+                      github.rest.issues.update({
+                          owner: context.repo.owner,
+                          repo: context.repo.repo,
+                          issue_number: context.payload.pull_request.number,
+                          milestone: null,
+                      });

.github/workflows/pull-request-post-merge-processing.yml

@@ -38,9 +38,7 @@ jobs:
               with:
                   php-version: '7.4'
             - name: 'Run the script to assign a milestone'
-              if: |
-                  !github.event.pull_request.milestone &&
-                  github.event.pull_request.base.ref == 'trunk'
+              if: github.event.pull_request.base.ref == 'trunk'
               run: php assign-milestone-to-merged-pr.php
               env:
                   PULL_REQUEST_ID: ${{ github.event.pull_request.node_id }}