Update freezegun requirement from <1.5,>=1.4.0 to >=1.4.0,<1.6

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@1.4.0...1.5.0)

---
updated-dependencies:
- dependency-name: freezegun
  dependency-type: direct:development
...

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

dev-requirements.txt

@@ -8,7 +8,7 @@ ddtrace==2.3.0
 docutils
 flake8
 flaky
-freezegun>=1.4.0,<1.5
+freezegun>=1.4.0,<1.6
 hypothesis
 ipdb
 mypy==1.4.1