Bump pip-tools from 5.3.1 to 6.1.0 in /requirements

Bumps [pip-tools](https://github.com/jazzband/pip-tools) from 5.3.1 to 6.1.0.
- [Release notes](https://github.com/jazzband/pip-tools/releases)
- [Changelog](https://github.com/jazzband/pip-tools/blob/master/CHANGELOG.md)
- [Commits](jazzband/pip-tools@5.3.1...6.1.0)

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

requirements/dev.txt

@@ -1,4 +1,4 @@
 -r app.txt
 pytest==6.2.*
 invoke==1.5.0
-pip-tools==5.3.1
+pip-tools==6.1.0