fix: add protobuf language id alias

[dimitropoulos]

• Add a test if possible
• Format all commit messages with Conventional Commits

• This PR fixes the protobuf id (common: used in linguist, highlight.js, and refractor) for protobuf code

• I have read docs for adding a theme.

• I have read docs for adding a language.
• I have searched around and this is the most up-to-date, actively maintained version of the language grammar.
• I have added a sample file that includes a variety of language syntaxes and succinctly captures the idiosyncrasy of a language. See docs for requirement.

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[octref]

LGTM, thanks!