Before this change, `cmd/bisync/testdata/bisync_vscode_debuggers_launch.json`
was in the repository, and every `-golden` run regenerated it from
`fstest/test_all/config.yaml`, adding unnecessary noise to commit diffs.
After this change, the file is in `.gitignore` and no longer tracked.
`-golden` still writes it locally, for copying debug configurations into
VS Code's `launch.json`.