Strip top-level dir if the repo source archive is not from googlesource (#1885)

Should fix
```
Resolved diffbase to c93dda2396e78fa74167b14c83b2468258e5d580
Cloning comparison repository...
curl -sSL https://github.com/bazelbuild/bazel/archive/c93dda2396e78fa74167b14c83b2468258e5d580.tar.gz -o /tmp/tmp4ioppk_9/repo.tar.gz
Setting up comparison repository...
set -e
sed -i.bak -e 's/^# android_sdk_repository/android_sdk_repository/' -e 's/^# android_ndk_repository/android_ndk_repository/' WORKSPACE.bzlmod
rm -f WORKSPACE.bzlmod.bak
rm -rf $HOME/bazeltest
mkdir $HOME/bazeltest
sed: can't read WORKSPACE.bzlmod: No such file or directory
```

https://buildkite.com/bazel/bazel-bazel-github-presubmit/builds/20266#018dcc2f-a232-4379-bdde-b8e46fb79524
1 file changed