Clean up partial clone before falling back to full clone

`RBS::Collection::Sources::Git#setup!` retries with a non-filtered
`git clone` when the `--filter=blob:none` variant fails. If the first
clone partially succeeded (e.g. the server returned HTTP 502 during
checkout), the cache directory is left non-empty, and the retry fails
with "destination path ... already exists and is not an empty
directory". Remove the directory before retrying so the fallback can
proceed.

Author: zonuexe

lib/rbs/collection/sources/git.rb

@@ -140,6 +140,12 @@ def to_lockfile
                 # git v2.27.0 or greater
                 git 'clone', '--filter=blob:none', remote, git_dir.to_s, chdir: nil
               rescue CommandError
+                # The failed `--filter=blob:none` clone may leave behind a
+                # partial repository (e.g. when the server returned an error
+                # mid-clone), which would cause the fallback `git clone` to
+                # fail with "destination path ... already exists and is not
+                # an empty directory". Clean it up before retrying.
+                FileUtils.rm_rf(git_dir)
                 git 'clone', remote, git_dir.to_s, chdir: nil
               end
             end