Bump go-github to pick up SearchType support

[kelsey-myers]

Summary

Bumps google/go-github to a pseudo-version off upstream master (google/go-github#4414), which adds SearchType support to SearchOptions/IssuesSearchResult.

Why

This is a prerequisite for making search_issues semantic by default (#2964) without a transport-level workaround. go-github only cuts full version releases, so this uses a commit-pinned pseudo-version rather than waiting on the next tag.

What changed

• go.mod/go.sum: google/go-github/v89 → v89.0.1-0.20260728185857-34349a88bac3
• Mechanical fixups for unrelated upstream API changes picked up by the bump:
  • IssueRequest split into CreateIssueRequest / UpdateIssueRequest; Issues.Edit renamed to Issues.Update
  • NewPullRequest renamed to CreatePullRequest
  • Label.Name / Label.Color changed from *string to string
• No behavior change on our side.

MCP impact

• No tool or API changes

Prompts tested (tool changes only)

N/A — no tool schema or behavior changes.

Security / limits

• No security or limits impact

Tool renaming

• I am not renaming tools as part of this PR

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Not needed

[Copilot]

Pull request overview

Bumps go-github to a commit containing issue search-type support and adapts code to upstream API changes.

Changes:

• Updates the go-github/v89 dependency.
• Migrates issue and pull-request request types and methods.
• Updates affected test fixtures.

Show a summary per file

File	Description
go.mod	Pins the new pseudo-version.
go.sum	Updates dependency checksums.
pkg/github/pullrequests.go	Adapts pull-request creation API.
pkg/github/issues.go	Adapts issue creation and update APIs.
pkg/github/issues_granular.go	Migrates granular issue operations.
pkg/github/issues_test.go	Updates issue fixtures and expectations.
pkg/github/issues_delete_test.go	Uses the new update request type.

Review details

• Files reviewed: 9/10 changed files
• Comments generated: 1
• Review effort level: Medium