[CI] Try installing protoc with script instead of apt

Summary: Try installing protoc with the same script we use for Buildkite agents.

Test Plan: It's annoying to test GitHub Actions workflows without creating a fork and whatnot. If this fails it should be easy to revert.

Reviewers: ashoat, tomek

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D6080