Fix duplicate entries in .git/config for GitHub PRs

[Copilot]

• Add focused regression tests for repeated and changed PR metadata associations
• Replace existing PR and base-branch metadata instead of appending values
• Run targeted tests, lint, and hygiene checks (compile, lint, and hygiene pass; extension-host execution is blocked by the unavailable VS Code Insiders download)
• Complete code review and security validation

• Fixes .git/config accumulates duplicate github-pr-owner-number/github-pr-base-branch entries instead of replacing them #8871

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[Alex Ross (alexr00)]

Copilot continue

[Copilot]

Copilot continue

Continued in 4fca727: serialized concurrent config updates, added regression coverage, and completed review/CodeQL. Compile, lint, and hygiene pass; extension-host execution remains blocked by DNS for the VS Code Insiders download.

[Copilot]

Pull request overview

This PR addresses issue #8871 where the extension’s PR/base-branch association metadata written into .git/config accumulates duplicate entries over time, by ensuring repeated associations don’t continually append additional values and by adding regression coverage for the expected behavior.

Changes:

• Add focused tests ensuring PR/base-branch metadata is replaced (not appended) across repeated calls and concurrent calls.
• Introduce a serialized setConfig helper to avoid concurrent update races and to prevent repeated appends when the effective value is already correct.
• Update associateBranchWithPullRequest and associateBaseBranchWithBranch to use the new helper.

Show a summary per file

File	Description
src/test/github/pullRequestGitHelper.test.ts	Adds regression tests for repeated/concurrent PR association and base-branch metadata replacement behavior.
src/github/pullRequestGitHelper.ts	Adds a serialized config update helper and routes PR/base-branch association writes through it to prevent unbounded duplicate config growth.

Review details

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• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite