Bump pillow from 8.1.0 to 8.1.1 in /tests (#9)

Bumps [pillow](https://github.com/python-pillow/Pillow) from 8.1.0 to 8.1.1.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](python-pillow/Pillow@8.1.0...8.1.1)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

tests/requirements.txt

@@ -1,6 +1,6 @@
 aiohttp==3.7.3
 foxglove-web==0.0.18
-pillow==8.1.0
+pillow==8.1.1
 coverage==5.4
 pygments==2.7.4
 pytest==6.2.2