build(deps): bump twisted in /testing/plugins_integration

Bumps [twisted](https://github.com/twisted/twisted) from 21.2.0 to 21.7.0.
- [Release notes](https://github.com/twisted/twisted/releases)
- [Changelog](https://github.com/twisted/twisted/blob/trunk/NEWS.rst)
- [Commits](twisted/twisted@twisted-21.2.0...twisted-21.7.0)

---
updated-dependencies:
- dependency-name: twisted
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

testing/plugins_integration/requirements.txt

@@ -11,5 +11,5 @@ pytest-rerunfailures==10.1
 pytest-sugar==0.9.4
 pytest-trio==0.7.0
 pytest-twisted==1.13.3
-twisted==21.2.0
+twisted==21.7.0
 pytest-xvfb==2.0.0