Copilot/migrate to api version 2026 03 10

[maxffarrell]

Adopts all breaking changes from the GitHub REST API version 2026-03-10, removing fields the API no longer returns and adding new ones.

Breaking field removals

• Repository: HasDownloads, MasterBranch, UseSquashPRTitleAsDefault
• Issue / IssueRequest: singular Assignee — use Assignees []string
• PullRequest: singular Assignee, MergeCommitSHA
• NewTeam: Permission
• CreateEvent / PushEventRepository: MasterBranch, HasDownloads
• Attestation: Bundle json.RawMessage → replaced by BundleURL *string

New fields

• AdvisoryCvssSeverities type (with CvssV3, CvssV4) added to DependabotSecurityAdvisory and SecurityAdvisory

Behavioral change

DeleteInstallation now returns HTTP 202 Accepted instead of 204 No Content. The implementation transparently handles AcceptedError as success so callers see no change.

Version bump

// github/github.go
defaultAPIVersion = "2026-03-10"  // was "2022-11-28"

---

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[codecov]

Codecov Report

❌ Patch coverage is 77.50000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.64%. Comparing base (39ef794) to head (b6ace06).
⚠️ Report is 59 commits behind head on master.

Files with missing lines	Patch %	Lines
example/verifyartifact/main.go	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4089      +/-   ##
==========================================
- Coverage   93.67%   93.64%   -0.03%     
==========================================
  Files         211      211              
  Lines       19478    19487       +9     
==========================================
+ Hits        18246    18249       +3     
- Misses       1034     1040       +6     
  Partials      198      198              

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[deiga]

@maxffarrell are you still working on this? Otherwise I could pick up some of the API changes into a separate PR

[maxffarrell]

@deiga haven't had time to work on this, going to close. If you could pick up that would be great!