> [...]

> (d) for archiving purposes in the public interest, scientific or historical research purposes or statistical purposes in accordance with Article 89(1) in so far as the right referred to in paragraph 1 is likely to render impossible or seriously impair the achievement of the objectives of that processing;

(emphasis mine)

I'd not say redacting a git repository does 'seriously impair' processing for archiving purposes. All the data (with the exception of the redacted e-mail) is still there, after all.

Still, the hashes will have changed, making the repo less useful for current users. But that has nothing to do with archival.