[deps] Bump freezegun from 1.2.1 to 1.5.1

Bumps [freezegun](https://github.com/spulec/freezegun) from 1.2.1 to 1.5.1.
- [Release notes](https://github.com/spulec/freezegun/releases)
- [Changelog](https://github.com/spulec/freezegun/blob/master/CHANGELOG)
- [Commits](spulec/freezegun@1.2.1...1.5.1)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements-test.txt

@@ -2,4 +2,4 @@ nose2[coverage_plugin]>=0.6.5
 responses~=0.18.0
 openwisp-utils[qa]~=1.0.5
 parameterized~=0.8.1
-freezegun==1.2.1
+freezegun==1.5.1