docs: using PrepareFetch::with_ref_name with non-branch refs causes panics

#2309

Author: decathorpe

gix/src/clone/access.rs

@@ -48,6 +48,9 @@ impl PrepareFetch {
     ///
     /// Note that `name` should be a partial name like `main` or `feat/one`, but can be a full ref name.
     /// If a branch on the remote matches, it will automatically be retrieved even without a refspec.
+    ///
+    /// **Warning**: Calling this method with a valid refspec that is not a branch name currently causes
+    /// subsequent calls to [`PrepareFetch::fetch_only`] or [`PrepareFetch::fetch_then_checkout`] to panic.
     pub fn with_ref_name<'a, Name, E>(mut self, name: Option<Name>) -> Result<Self, E>
     where
         Name: TryInto<&'a gix_ref::PartialNameRef, Error = E>,