Support nested GitLab groups in issue ref parsing

[akashgit]

Minor edge case from PR #210 review: parse_issue_ref captures owner/repo with [^/]+/[^/]+, which won't handle GitLab's nested group structure like group/subgroup/project.

Example

https://gitlab.com/group/subgroup/project/-/issues/42

Currently fails to parse. The regex should allow multiple path segments before /-/issues/.

Low priority — most GitLab projects use a single group level.

Refs: PR #210

[akashgit]

Fixed in PR #213.

The GitLab URL regex in parse_issue_ref was changed from [^/]+/[^/]+ to .+? for the owner/repo capture group, so nested groups like group/subgroup/project are parsed correctly:

# Before: only matched group/project
r"https?://([^/]+)/([^/]+/[^/]+)/-/issues/(\d+)"

# After: matches group/subgroup/project (any depth)
r"https?://([^/]+)/(.+?)/-/issues/(\d+)"

Test coverage includes https://gitlab.com/group/subgroup/project/-/issues/12 and self-hosted GitLab instances (gitlab.ibm.com).