Fix possible double normalization of hardware field (#3462)

It seems to happen in the very simple workflow, e.g. `tmt run discover plan --name '...'`.

tmt/steps/provision/__init__.py

@@ -632,7 +632,7 @@ def format(self) -> Iterator[tuple[str, str, str]]:
 
 def normalize_hardware(
         key_address: str,
-        raw_hardware: Optional[tmt.hardware.Spec],
+        raw_hardware: Union[None, tmt.hardware.Spec, tmt.hardware.Hardware],
         logger: tmt.log.Logger) -> Optional[tmt.hardware.Hardware]:
     """
     Normalize a ``hardware`` key value.
@@ -645,6 +645,9 @@ def normalize_hardware(
     if raw_hardware is None:
         return None
 
+    if isinstance(raw_hardware, tmt.hardware.Hardware):
+        return raw_hardware
+
     # From command line
     if isinstance(raw_hardware, (list, tuple)):
         merged: dict[str, Any] = {}