Convert Roomba hw_version to string for device registry (home-assistant#172497)

Author: frenck

homeassistant/components/roomba/entity.py

@@ -29,7 +29,11 @@ def __init__(self, roomba, blid) -> None:
             model=self.vacuum_state.get("sku"),
             name=str(self.vacuum_state.get("name")),
             sw_version=self.vacuum_state.get("softwareVer"),
-            hw_version=self.vacuum_state.get("hardwareRev"),
+            hw_version=(
+                str(hw_rev)
+                if (hw_rev := self.vacuum_state.get("hardwareRev")) is not None
+                else None
+            ),
         )
 
         if mac_address := self.vacuum_state.get("hwPartsRev", {}).get(