build(deps): bump pytz from 2021.1 to 2021.3 in /tools (#1133)

Bumps [pytz](https://github.com/stub42/pytz) from 2021.1 to 2021.3.
- [Release notes](https://github.com/stub42/pytz/releases)
- [Commits](stub42/pytz@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>

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

Author: dependabot[bot]

tools/requirements.txt

@@ -1,7 +1,7 @@
 aiohttp==3.7.4
 async-timeout==3.0.1
 logbook==1.5.3
-pytz==2021.1
+pytz==2021.3
 raven==6.10.0
 structlog==21.1.0
 taskcluster==44.2.2