workflows/periodic-merge: update haskell-updates PR's base branch (#523160)

.github/workflows/periodic-merge-24h.yml

@@ -22,7 +22,7 @@ defaults:
 
 jobs:
   periodic-merge:
-    if: github.repository_owner == 'NixOS'
+    if: github.repository_owner == 'NixOS' || github.event_name == 'workflow_dispatch'
     strategy:
       # don't fail fast, so that all pairs are tried
       fail-fast: false
@@ -49,3 +49,34 @@ jobs:
     name: ${{ matrix.pairs.name || format('{0} → {1}', matrix.pairs.from, matrix.pairs.into) }}
     secrets:
       NIXPKGS_CI_APP_PRIVATE_KEY: ${{ secrets.NIXPKGS_CI_APP_PRIVATE_KEY }}
+
+  # Resets the target branch of the current haskell-updates PR.
+  # This makes GitHub hide all the commits that are already part of staging and gives us a much clearer PR view.
+  haskell-updates:
+    needs: periodic-merge
+    runs-on: ubuntu-slim
+    permissions:
+      pull-requests: write
+    steps:
+      - name: Find PR and update target branch
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
+        with:
+          script: |
+            // There will at most be a single haskell-updates PR anyway, so no need to paginate.
+            await Promise.all(
+              (
+                await github.rest.pulls.list({
+                  ...context.repo,
+                  state: 'open',
+                  head: `${context.repo.owner}:haskell-updates`,
+                })
+              ).data.map((pr) =>
+                github.rest.pulls.update({
+                  ...context.repo,
+                  pull_number: pr.number,
+                  // Just updating to the same branch to trigger a UI update.
+                  // This is staging most of the time, but could be staging-next in rare cases.
+                  base: pr.base.ref,
+                }),
+              ),
+            )

.github/workflows/periodic-merge-6h.yml

@@ -22,7 +22,7 @@ defaults:
 
 jobs:
   periodic-merge:
-    if: github.repository_owner == 'NixOS'
+    if: github.repository_owner == 'NixOS' || github.event_name == 'workflow_dispatch'
     strategy:
       # don't fail fast, so that all pairs are tried
       fail-fast: false