fix: don't modify config of external repos

The git config files of external repos are read-only.

This is the only place where we make reference to a remote named
'origin', so this also closes kemitix/git-next#85.

Closes kemitix/git-next#85

crates/git/src/repo_details.rs

@@ -138,7 +138,7 @@ impl RepoDetails {
     #[tracing::instrument]
     pub fn write_remote_url(&self, url: &RemoteUrl) -> Result<(), kxio::fs::Error> {
         if self.gitdir.storage_path_type() != StoragePathType::Internal {
-            // return Err(Not an internal repo)
+            return Ok(());
         }
         let fs = self.gitdir.as_fs();
         // load config file