Add workflow for automatically rebasing open PRs (#2612)

Introduce a workflow that's reponsible for automatically rebasing open
PRs when a commit has landed in the default (e.g. master) branch. Ensure
a comment is posted on that PR when the rebasing action job has failed.

Signed-off-by: timflannagan <timflannagan@gmail.com>

.github/workflows/rebase.yaml

@@ -0,0 +1,20 @@
+name: rebase pull request
+on:
+ push:
+ branches:
+ - master
+jobs:
+ rebase:
+ runs-on: ubuntu-latest
+ steps:
+ - uses: peter-evans/rebase@v1
+ with:
+ base: master
+ - name: Send failure message
+ uses: peter-evans/create-or-update-comment@v1
+ if: ${{ failure() }}
+ with:
+ issue-number: ${{ github.event.issue.number || github.event.number }}
+ body: |
+ Automatic rebasing for this PR has failed. You'll need to manually
+ rebase against the default branch.