Bump filelock from 3.15.4 to 3.20.1 in /requirements

Bumps [filelock](https://github.com/tox-dev/py-filelock) from 3.15.4 to 3.20.1.
- [Release notes](https://github.com/tox-dev/py-filelock/releases)
- [Changelog](https://github.com/tox-dev/filelock/blob/main/docs/changelog.rst)
- [Commits](tox-dev/filelock@3.15.4...3.20.1)

---
updated-dependencies:
- dependency-name: filelock
  dependency-version: 3.20.1
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/dev.txt

@@ -14,7 +14,7 @@ colorama==0.4.6
     # via tox
 distlib==0.3.8
     # via virtualenv
-filelock==3.15.4
+filelock==3.20.1
     # via
     #   tox
     #   virtualenv