ci: only run changelog job on tag (argoproj#6003)

Signed-off-by: Alex Collins <[email protected]>

.github/workflows/changelog.yaml

@@ -1,28 +1,25 @@
 name: Changelog
 
 on:
- # we not need or want to run on on pull request or branch changes, we just need to run periodically
- # run every hour to make sure it is up-to-date
- schedule:
- - cron: "0 * * * *"
+ push:
+  tags:
+  - v*
+  - "!v0.0.0"
 jobs:
  generate_changelog:
  runs-on: ubuntu-latest
  name: Generate changelog
  steps:
  - uses: actions/checkout@v2
  with:
+ ref: master
  fetch-depth: 0
  - run: git fetch --prune --prune-tags
  - run: git tag -l 'v*'
- # avoid invoking `make` to reduce the change of Makefile problem failing this workflow
+ # avoid invoking `make` to reduce the risk of a Makefile bug failing this workflow
  - run: ./hack/changelog.sh > CHANGELOG.md
  - uses: peter-evans/create-pull-request@v3
  with:
  title: 'docs: updated CHANGELOG.md'
  commit-message: 'docs: updated CHANGELOG.md'
- signoff: true
- env:
- # we need to use a token, otherwise the required build jobs will not run
- # https://github.com/peter-evans/create-pull-request/issues/48
- GITHUB_TOKEN: ${{ secrets.CREATE_PULL_REQUEST_TOKEN }}
+ signoff: true