Don't cache target in target_history (#1791)

* Don't cache target in target_history

* Don't cache target

* unit tests

* Add release note

qiskit_ibm_runtime/ibm_backend.py

@@ -333,9 +333,9 @@ def target(self) -> Target:
         Returns:
             Target
         """
-        self._get_properties()
+        self._get_properties(datetime=python_datetime.now())
         self._get_defaults()
-        self._convert_to_target()
+        self._convert_to_target(refresh=True)
         return self._target
 
     def target_history(self, datetime: Optional[python_datetime] = None) -> Target:

release-notes/unreleased/1791.bug.rst

@@ -0,0 +1,2 @@
+Fixed an issue where calling :meth:`IBMBackend.target_history` would cache the backend target and
+then calling :meth:`IBMBackend.target` would incorrectly return that cached target.

test/unit/mock/fake_runtime_client.py

@@ -455,8 +455,6 @@ def backend_status(self, backend_name: str) -> Dict[str, Any]:
 
     def backend_properties(self, backend_name: str, datetime: Any = None) -> Dict[str, Any]:
         """Return the properties of a backend."""
-        if datetime:
-            raise NotImplementedError("'datetime' is not supported.")
         if ret := self._find_backend(backend_name).properties:
             return ret.copy()
         return None