add closing dependabot step

[derrickaw]

1. Excluded paths are ignored by dependabot for vulnerabilities - see open issue exclude-paths should also suppress security update PRs dependabot/dependabot-core#14408.
2. Adding a workflow step to close dependabot PRs that touch generated requirements files that still pop up due to vulnerabilities.
3. Once above issue is fixed, we can remove this step.

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[Abacn]

Thanks, this is a good idea. However it sounds like better fit PR bot's responsibiliy:

https://github.com/apache/beam/blob/master/.github/workflows/pr-bot-new-prs.yml

PreCommit_GHA is to make sure GitHub Action workflow's formatting and enforcement (enforce documentation, trigger path, disallow gsutil etc)

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[Abacn]

Thanks!