Bump gidgethub from 4.1.1 to 4.2.0 (#415)

Bumps [gidgethub](https://github.com/brettcannon/gidgethub) from 4.1.1 to 4.2.0.
- [Release notes](https://github.com/brettcannon/gidgethub/releases)
- [Changelog](https://github.com/brettcannon/gidgethub/blob/master/docs/changelog.rst)
- [Commits](gidgethub/gidgethub@v4.1.1...v4.2.0)

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Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Mariatta <Mariatta@users.noreply.github.com>

Author: dependabot-preview[bot]

requirements.txt

@@ -1,6 +1,6 @@
 cherry_picker==1.3.2
 aiohttp==3.7.3
-gidgethub==4.1.1
+gidgethub==4.2.0
 cachetools==4.1.1
 redis==3.5.3
 celery==5.0.4