Bump aiohttp from 3.7.2 to 3.7.3 (#414)

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 3.7.2 to 3.7.3.
- [Release notes](https://github.com/aio-libs/aiohttp/releases)
- [Changelog](https://github.com/aio-libs/aiohttp/blob/master/CHANGES.rst)
- [Commits](aio-libs/aiohttp@v3.7.2...v3.7.3)

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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>

requirements.txt

@@ -1,5 +1,5 @@
 cherry_picker==1.3.2
-aiohttp==3.7.2
+aiohttp==3.7.3
 gidgethub==4.1.1
 cachetools==4.1.1
 redis==3.5.3