Bump pytz from 2021.1 to 2021.3

Bumps [pytz](https://github.com/stub42/pytz) from 2021.1 to 2021.3.
- [Release notes](https://github.com/stub42/pytz/releases)
- [Commits](https://github.com/stub42/pytz/compare/release_2021.1...release_2021.3)

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

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

requirements.txt

@@ -1,6 +1,6 @@
 asgiref==3.4.1
 Django==3.2.7
-pytz==2021.1
+pytz==2021.3
 sqlparse==0.4.2
 requests==2.26.0
 python-slugify==5.0.2