chore: bump sanic from 20.12.3 to 20.12.6 in /requirements (cloudevents#155)

Bumps [sanic](https://github.com/sanic-org/sanic) from 20.12.3 to 20.12.6.
- [Release notes](https://github.com/sanic-org/sanic/releases)
- [Changelog](https://github.com/sanic-org/sanic/blob/main/CHANGELOG.rst)
- [Commits](sanic-org/sanic@v20.12.3...v20.12.6)

---
updated-dependencies:
- dependency-name: sanic
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Grant Timmerman <744973+grant@users.noreply.github.com>
Co-authored-by: Yurii Serhiichuk <xSAVIKx@users.noreply.github.com>

Author: 3 people

requirements/test.txt

@@ -6,7 +6,7 @@ flake8-strict
 pytest
 pytest-cov
 # web app tests
-sanic<=20.12.4; python_version <= '3.6'
+sanic<=20.12.6; python_version <= '3.6'
 sanic; python_version > '3.6'
 sanic-testing; python_version > '3.6'
 aiohttp