Ignore mypy error about rrule frequency type

Mypy expects a Literal for the `freq` argument of `rrule.rrule`, but
it can't infer that the values from the `_RRULE_FREQ_MAP` dictionary are of
the correct type. We add a `# type: ignore[arg-type]` comment to suppress
the error.

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

src/frequenz/client/dispatch/recurrence.py

@@ -211,7 +211,10 @@ def _as_rrule(self, start_time: datetime) -> rrule.rrule:
             until = end.until
 
         rrule_obj = rrule.rrule(
-            freq=_RRULE_FREQ_MAP[self.frequency],
+            # Mypy expects a Literal for the `freq` argument, but it can't infer
+            # that the values from the `_RRULE_FREQ_MAP` dictionary are of the
+            # correct type.
+            freq=_RRULE_FREQ_MAP[self.frequency],  # type: ignore[arg-type]
             dtstart=start_time,
             count=count,
             until=until,