Fix source string in hugging face installs with subfolders

Author: brandonrising

invokeai/app/services/model_install/model_install_common.py

@@ -103,7 +103,7 @@ def __str__(self) -> str:
         if self.variant:
             base += f":{self.variant or ''}"
         if self.subfolder:
-            base += f":{self.subfolder}"
+            base += f"::{self.subfolder}"
         return base