worktree: Disable flaky tests (test_write_file, test_git_status_postprocessing) (#26710)

Comment out flaky tests:
- `worktree_tests::test_write_file`
- `worktree_tests::test_git_status_postprocessing`

Job links:
- windows fail:
https://github.com/zed-industries/zed/actions/runs/13841766606/job/38730766252
- macos fail:
https://github.com/zed-industries/zed/actions/runs/13841766606/job/38730764118

That
[commit](https://github.com/zed-industries/zed/commit/85384fb9c67614795a82f5b0a09895875beb16d0)
was a non-op script change, but in the [prior
commit](https://github.com/zed-industries/zed/commit/00359271d11b6ba865fe81f04f675bf588a17335)
[windows/macos
pass](https://github.com/zed-industries/zed/actions/runs/13841135221).

Similar experience with `worktree_tests::test_write_file` on both macOS
windows too.

- See also: https://github.com/zed-industries/zed/pull/26684

Release Notes:

- N/A