Bump testfixtures from 6.18.5 to 7.0.4

Bumps [testfixtures](https://github.com/Simplistix/testfixtures) from 6.18.5 to 7.0.4.
- [Release notes](https://github.com/Simplistix/testfixtures/releases)
- [Changelog](https://github.com/simplistix/testfixtures/blob/master/CHANGELOG.rst)
- [Commits](simplistix/testfixtures@6.18.5...7.0.4)

---
updated-dependencies:
- dependency-name: testfixtures
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

test-requirements.txt

@@ -1,4 +1,4 @@
 factory-boy>=2.4
-testfixtures==6.18.5
+testfixtures==7.0.4
 psycopg2>=2.5.4
 mysqlclient>=1.3.3