This only updates to Go 1.21 baseline, which is what the module still
specifies as the minimum version. I'll need to run this again when
moving to Go 1.25 or 1.26 as minimum.
When GitHub creates patches for Dependabot PRs, it generates a "From:"
line that is not valid according to RFC 5322: the address spec contains
unquoted special characters (the "[bot]" in "dependabot[bot]"). While
the 'net/mail' parser makes some exceptions to the spec, this is not one
of them, so parsing these patch headers fails.
Git's 'mailinfo' command avoids this by only implementing the unquoting
part of RFC 5322 and then applying a heuristic to separate the string in
to name and email values that seem reasonable.
This commit does two things:
1. Reimplements ParsePatchIdentity to follow Git's logic, so that it can
accept a wider range of inputs, including quoted strings. Strings
accepted by the previous implementation parse in the same way with
one exception: inputs that contain whitespace inside the angle
brackets for an email address now use the email address as the name
and drop any separate name component.
2. When parsing mail-formatted patches, use ParsePatchIdentity to parse
the "From:" line instead of the 'net/mail' function.
Billy Keyes