build(deps): bump pytest-mock in /testing/plugins_integration

Bumps [pytest-mock](https://github.com/pytest-dev/pytest-mock) from 3.4.0 to 3.5.1.
- [Release notes](https://github.com/pytest-dev/pytest-mock/releases)
- [Changelog](https://github.com/pytest-dev/pytest-mock/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest-mock/compare/v3.4.0...v3.5.1)

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

testing/plugins_integration/requirements.txt

@@ -6,7 +6,7 @@ pytest-cov==2.10.1
 pytest-django==4.1.0
 pytest-flakes==4.0.3
 pytest-html==3.1.1
-pytest-mock==3.4.0
+pytest-mock==3.5.1
 pytest-rerunfailures==9.1.1
 pytest-sugar==0.9.4
 pytest-trio==0.7.0