bugfix: don't overwrite the cached container

nf_core/pipelines/download.py

@@ -1311,7 +1311,7 @@ def singularity_copy_library_image(
     ) -> None:
         """Copy Singularity image from NXF_SINGULARITY_LIBRARYDIR to target folder, and possibly NXF_SINGULARITY_CACHEDIR."""
         self.singularity_copy_image(container, library_path, out_path)
-        if cache_path:
+        if cache_path and not os.path.exists(cache_path):
             self.singularity_copy_image(container, library_path, cache_path)
 
     def singularity_copy_image(self, container: str, from_path: str, to_path: str) -> None: