Fix overflowing integer when retrieving comments for FCP

[apiraino]

This is a patch I've been using locally since long, should be the final nail in the coffin to fix the overflowing GH ID issue we started experiencing a while ago.

I'd like to upstream it after some testing.

[Mark-Simulacrum]

Might want to switch to u64 to preempt another round of problems.

[apiraino]

Note for myself to investigate before merge: using u64 causes a runtime error when retrieving issues

2025-02-26T16:29:55.830555Z DEBUG triagebot::github: send_req with RequestBuilder { method: GET, url: Url { scheme: "https", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("api.github.com")), port: None, path: "/search/issues", query: Some("q=state:open+no:assignee+label:T-compiler+label:P-critical+repo:rust-lang/rust&sort=created&order=asc&per_page=100&page=1"), fragment: None }, headers: {"user-agent": "rust-lang-triagebot", "authorization": Sensitive} }
...
Error: out of range integral type conversion attempted

The error happens here and it's due to parsing the JSON that goes into IssueSearchResult.issues which is a Vec<Issue>, so there must be some integer casting that fails inside there