Bot is reporting invalid `.repo-metadata.json` files generated for Rust

Some bot in the SDK Platform opened this bug:

https://github.com/googleapis/google-cloud-rust/issues/1859

I would close it as non-actionable, but past experience says the robots will just open it again. Since these files are generated by librarian the problems are either (a) librarian is generating bad files, or (b) the bot is expecting the wrong thing in these files. Either way, seems like the fixes should happen in the SDK Platform world?

I know we want to get rid of the files, but until we do, they should be correct, no?

Start with the linked googleapis/google-cloud-rust#1859 report, then trace how librarian generates .repo-metadata.json for Rust and compare that output with the bot's expectations. Done means determining whether librarian or the bot is wrong and identifying the corresponding fix scope, with the invalid-report loop resolved.

Written by the indexing model from the issue text.