[deps] Update freezegun requirement from ~=1.5.4 to ~=1.5.5

Updates the requirements on [freezegun](https://github.com/spulec/freezegun) to permit the latest version.
- [Release notes](https://github.com/spulec/freezegun/releases)
- [Changelog](https://github.com/spulec/freezegun/blob/master/CHANGELOG)
- [Commits](spulec/freezegun@1.5.4...1.5.5)

---
updated-dependencies:
- dependency-name: freezegun
  dependency-version: 1.5.5
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements-test.txt

@@ -1,5 +1,5 @@
 responses~=0.25.8
-freezegun~=1.5.4
+freezegun~=1.5.5
 # Needed to test integrations
 openwisp-monitoring @ https://github.com/openwisp/openwisp-monitoring/tarball/1.2
 openwisp-controller @ https://github.com/openwisp/openwisp-controller/tarball/1.2