Renaming a dir to the same name fails if it's not empty on overlay mounts

$ t="$(mktemp -d)"
$ monty -m "${t}::/mnt::overlay" -c "import os; os.mkdir('/mnt/foo'); open('/mnt/foo/x','w').close(); os.rename('/mnt/foo','/mnt/foo')"
error: Traceback (most recent call last):
  File "<string>", line 1, in <module>
    import os; os.mkdir('/mnt/foo'); open('/mnt/foo/x','w').close(); os.rename('/mnt/foo','/mnt/foo')
                                                                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
OSError: [Errno 39] Directory not empty: '/mnt/foo'
$ echo $?
1

$ t="$(mktemp -d)"
$ python -c "import os; os.mkdir('${t}/foo'); open('${t}/foo/x','w').close(); os.rename('${t}/foo','${t}/foo')"
$ echo $?
0

diff --git a/crates/monty-fs/src/overlay.rs b/crates/monty-fs/src/overlay.rs
index dd3375e6..5961ee7f 100644
--- a/crates/monty-fs/src/overlay.rs
+++ b/crates/monty-fs/src/overlay.rs
@@ -1082,6 +1082,11 @@ fn rename(
         None => host_is_dir(ctx.mount_dir, resolve_real(src_vpath, ctx)?.for_dir_op()),
     };

+    // A self-rename is a no-op on every POSIX system regardless of contents
+    if src_rel == dst_rel {
+        return Ok(MontyObject::none());
+    }
+
     reject_rename_type_mismatch(state, &dst_rel, src_is_dir, ctx, dst_vpath)?;

     // Renaming a directory onto an existing non-empty directory must fail,