Bump pytz from 2026.2 to 2026.3.post1 (#466)

Bumps [pytz](https://github.com/stub42/pytz) from 2026.2 to 2026.3.post1.
- [Release notes](https://github.com/stub42/pytz/releases)
- [Commits](stub42/pytz@release_2026.2...release_2026.3.post1)

---
updated-dependencies:
- dependency-name: pytz
  dependency-version: 2026.3.post1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -40,7 +40,7 @@ pytest==9.1.1
 pytest-cov==7.1.0
 pytest-django==4.12.0
 python-discovery==1.4.4
-pytz==2026.2
+pytz==2026.3.post1
 PyYAML==6.0.3
 rcssmin==1.2.1
 referencing==0.37.0