feat: adds letmaik.git-tree-compare to extensions

[mikeytown19]

• I have read the note above about PRs contributing or fixing extensions
• I have tried reaching out to the extension maintainers about publishing this extension to Open VSX (if not, please create an issue in the extension's repo using this template).
• This extension has an OSI-approved OSS license (we don't accept proprietary extensions in this repository)

Description

This PR adds letmaik.git-tree-compare to the auto-publish list to make the Git Tree Compare extension available on Open VSX.

Why this extension should be included:

• MIT licensed (OSI-approved open source)
• Popular extension with 220,083+ installs on VS Code Marketplace
• Provides valuable git diff visualization in tree format
• Currently unavailable to Cursor/Open VSX users
• Author has not responded to request for direct publishing (link to issue)

The extension helps developers compare their working tree against branches, tags, or commits in a folder tree structure, which is especially useful for pull request preparation.