Bump protobuf from 3.1.0 to 3.18.3 in /website

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.1.0 to 3.18.3.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/generate_changelog.py)
- [Commits](protocolbuffers/protobuf@v3.1.0...v3.18.3)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-type: direct:production
...

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

website/requirements.txt

@@ -10,7 +10,7 @@ djangorestframework-jwt==1.8.0
 httmock==1.2.6
 humanize==0.5.1
 idna==2.7
-protobuf==3.1.0
+protobuf==3.18.3
 psycopg2==2.8.5
 PyJWT==1.4.2
 pyyaml==4.2b1