Fix: GPv3 layer renaming when name is unchanged

When old and new names of layers/groups are same, garbage string is
displayed. This is because `oldname` char pointer is referenced to
`node.name`. After function execution, `oldname` memory is freed in
`interface_handler` (see `after.rename_orig`), thus displays garbage
string.
Fix is to copy the content of `oldname` instead of referencing it.

Pull Request: https://projects.blender.org/blender/blender/pulls/111173

source/blender/editors/space_outliner/outliner_draw.cc

@@ -864,8 +864,10 @@ static void namebutton_fn(bContext *C, void *tsep, char *oldname)
           /* The node already has the new name set. To properly rename the node, we need to first
            * store the new name, restore the old name in the node, and then call the rename
            * function. */
+
           std::string new_name(node.name);
-          node.name = oldname;
+          node.name = BLI_strdup(oldname);
+
           if (node.is_group()) {
             grease_pencil.rename_group(node.as_group_for_write(), new_name);
           }