Bump mock from 0.8 to 4.0.3

Bumps [mock](https://github.com/testing-cabal/mock) from 0.8 to 4.0.3.
- [Release notes](https://github.com/testing-cabal/mock/releases)
- [Changelog](https://github.com/testing-cabal/mock/blob/master/CHANGELOG.rst)
- [Commits](testing-cabal/mock@0.8.0...4.0.3)

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

requirements-test.txt

@@ -1,5 +1,5 @@
 # test runs requirements (versions we'll be testing against) - automatically updated
-mock==0.8
+mock==4.0.3
 pytest==6.2.4  # tests framework used
 pytest-cov==2.11.1  # coverage reports to verify tests quality
 coverage==5.5 # pytest-cov