Fix rm permission errors in local tests

[grodowski]

Do not attempt to recreate the .gopath symlink every time tests run. Fixes script/test failing locally with numerous toolchain permission errors from L14:

rm: cannot remove '.gopath/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.0.darwin-arm64/src/debug/buildinfo/testdata/go117/go117.base64': Permission denied

A more comprehensive fix could remove the symlink setup entirely.

[Copilot]

Pull request overview

Updates the local test/bootstrap workflow to avoid repeatedly deleting and recreating the repo-local .gopath, preventing local script/test runs from failing due to permission errors when removing files in .gopath/pkg/mod (notably Go toolchain module contents).

Changes:

• Only recreate .gopath (and the src/github.com/github/gh-ost symlink) when the expected symlink is missing.
• Preserve existing .gopath across repeated test runs to avoid rm -rf permission failures.

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[Copilot]

The guard only checks that .gopath/src/github.com/github/gh-ost is a symlink (-L). If the repo is moved/renamed, an existing symlink can become stale (or point at a different checkout) and this block will be skipped, causing script/test/script/go to cd into the wrong/broken location. Consider also verifying the symlink target matches the current repo path (e.g., compare readlink to $PWD and/or ensure the link target exists) and recreate .gopath when it doesn't.