test(git): close test repositories instead of rmtree so teardown works on Windows

[tsurutanmen]

Description

On Windows, 40 of the 87 tests in src/git error during teardown of the test_repository fixture. The assertions pass, but pytest reports PermissionError from shutil.rmtree(repo_path):

• [WinError 32] (file in use): GitPython still holds handles, such as its persistent git cat-file processes, when the fixture removes the directory.
• [WinError 5] (access denied): git writes loose object files as read-only, and shutil.rmtree cannot delete read-only files on Windows. This shows up in the two git_add tests, where the git CLI writes the objects.

This PR calls test_repo.close() to release the handles, and drops the explicit rmtree. The repository lives under pytest's tmp_path, and pytest removes that directory itself, including read-only files.

Server Details

• Server: git
• Changes to: tests only

Motivation and Context

Contributors on Windows currently see 40 errors from a clean checkout. That makes it hard to tell whether a change broke anything.

How Has This Been Tested?

On Windows 11, Python 3.11, git for Windows:

• before: 47 passed, 40 errors
• after: 47 passed

ruff check and pyright are clean. There are no behavior changes on Linux or macOS: close() is a no-op there apart from releasing resources, and tmp_path cleanup already applies.

Breaking Changes

None. Only tests change.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Protocol Documentation
• My changes follows MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context

I found this while working on #4879, which also touches this server.

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