Bump firebase-admin from 6.3.0 to 6.4.0

Bumps [firebase-admin](https://github.com/firebase/firebase-admin-python) from 6.3.0 to 6.4.0.
- [Release notes](https://github.com/firebase/firebase-admin-python/releases)
- [Commits](firebase/firebase-admin-python@v6.3.0...v6.4.0)

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

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

requirements.txt

@@ -20,7 +20,7 @@ djangorestframework==3.14.0
 djangorestframework-camel-case==1.4.2
 docutils==0.20.1
 drf-yasg[validation]==1.21.7
-firebase-admin==6.3.0
+firebase-admin==6.4.0
 flower==2.0.1
 gunicorn[gevent]==21.2.0
 hexbytes==0.3.1