Fix non-metric atmospheric pressure in Open Weather Map (#49030)

The openweathermap component retrieves atmospheric pressure from the
openweathermap api and passes it along without checking the units.
The api returns pressure in metric (hPa).  If you the use the weather
forecast card on a non-metric home assistant install, you will then
see the pressure reported as something like '1019 inHg', which is an
incorrect combination of metric value and non-metric label.

To fix this, check when retrieving the pressure if this is a metric
system.  If not, convert the value to non-metric inHg before sending
it along.

Weirdly, this isn't a problem for temperature, so I suspect temp is
getting converted somewhere else.

homeassistant/components/openweathermap/weather.py

@@ -1,6 +1,7 @@
 """Support for the OpenWeatherMap (OWM) service."""
 from homeassistant.components.weather import WeatherEntity
-from homeassistant.const import TEMP_CELSIUS
+from homeassistant.const import PRESSURE_HPA, PRESSURE_INHG, TEMP_CELSIUS
+from homeassistant.util.pressure import convert as pressure_convert
 
 from .const import (
     ATTR_API_CONDITION,
@@ -82,7 +83,12 @@ class OpenWeatherMapWeather(WeatherEntity):
     @property
     def pressure(self):
         """Return the pressure."""
-        return self._weather_coordinator.data[ATTR_API_PRESSURE]
+        pressure = self._weather_coordinator.data[ATTR_API_PRESSURE]
+        # OpenWeatherMap returns pressure in hPA, so convert to
+        # inHg if we aren't using metric.
+        if not self.hass.config.units.is_metric and pressure:
+            return pressure_convert(pressure, PRESSURE_HPA, PRESSURE_INHG)
+        return pressure
 
     @property
     def humidity(self):