Some very small fixes (#590)

- Resampling: Reuse existing variable.
- PvPowerFormula: Fix comment typo

Author: Marenz

src/frequenz/sdk/actor/_resampling.py

@@ -79,7 +79,7 @@ async def _subscribe(self, request: ComponentMetricRequest) -> None:
 
         # This is a temporary hack until the Sender implementation uses
         # exceptions to report errors.
-        sender = self._channel_registry.new_sender(request.get_channel_name())
+        sender = self._channel_registry.new_sender(request_channel_name)
 
         async def sink_adapter(sample: Sample[Quantity]) -> None:
             await sender.send(sample)

src/frequenz/sdk/timeseries/_formula_engine/_formula_generators/_pv_power_formula.py

@@ -40,7 +40,7 @@ def generate(self) -> FormulaEngine[Power]:
                 "Subscribing to the resampling actor with a non-existing "
                 "component id, so that `0` values are sent from the formula."
             )
-            # If there are no PV inverters, we have to send 0 values as the same
+            # If there are no PV inverters, we have to send 0 values at the same
             # frequency as the other streams.  So we subscribe with a non-existing
             # component id, just to get a `None` message at the resampling interval.
             builder.push_component_metric(