ci(mergify): only dismiss own review approvals (backport #1146)

[mergify]

This is an automatic backport of pull request #1146 done by Mergify.
Cherry-pick of b7bf954 has failed:

On branch mergify/bp/cryostat-v2.2/pr-1146
Your branch is up to date with 'origin/cryostat-v2.2'.

You are currently cherry-picking commit b7bf9545.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .mergify.yml

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[github-actions]

Hi @mergify[bot]! Add at least one of the required labels to this PR

Required labels are : chore,ci,cleanup,docs,feat,fix,perf,refactor,style,test