[8.13](backport #39299) Fix the annotating for snapshot and staging

[mergify]

Proposed commit message

This commit adds the --append flag to the buildkite-annotate so that when it is called by the snapshot and staging steps will not overwrite the other annotation.

---

This is an automatic backport of pull request #39299 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of f6bad74 has failed:

On branch mergify/bp/8.13/pr-39299
Your branch is up to date with 'origin/8.13'.

You are currently cherry-picking commit f6bad74ef6.
  (fix conflicts and run "git cherry-pick --continue")
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Unmerged paths:
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	deleted by us:   .buildkite/scripts/dra.sh

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[botelastic]

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[elasticmachine]

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[dliappis]

Closing as it's been cherry-picked in #39198