Fix bisecting into rollups via unrolled perf builds

[lqd]

The perfbot comment on rollups has recently changed format, breaking the commit extraction from that comment.

Also updates proc-macro2 to fix build errors on nightly.

Now uses a regex to look for the shas found in the perf table column, to support both formats:

• https://github.com/rust-lang/rust/pull/113014#issuecomment-1605868471
• https://github.com/rust-lang/rust/pull/113105#issuecomment-1610393473

[lqd]

Converting to draft to make more changes: the parsing here needs to be backwards compatible with the prior format.

[lqd]

I've added the 2 linked examples as tests. Should be ready now.