Bump mysqlclient from 2.2.4 to 2.2.6 in /requirements (#1423)

Bumps [mysqlclient](https://github.com/PyMySQL/mysqlclient) from 2.2.4 to 2.2.6.
- [Release notes](https://github.com/PyMySQL/mysqlclient/releases)
- [Changelog](https://github.com/PyMySQL/mysqlclient/blob/main/HISTORY.rst)
- [Commits](PyMySQL/mysqlclient@v2.2.4...v2.2.6)

---
updated-dependencies:
- dependency-name: mysqlclient
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

requirements/mysql.txt

@@ -1 +1 @@
-mysqlclient==2.2.4
+mysqlclient==2.2.6