Fix executor being overloaded in caldav (#112084)

Migrate to using a single executor job instead of creating
one per calendar. If the user had a lot of calendars the
executor would get overloaded

homeassistant/components/caldav/api.py

@@ -1,6 +1,5 @@
 """Library for working with CalDAV api."""
 
-import asyncio
 
 import caldav
 
@@ -13,20 +12,13 @@ async def async_get_calendars(
     """Get all calendars that support the specified component."""
 
     def _get_calendars() -> list[caldav.Calendar]:
-        return client.principal().calendars()
-
-    calendars = await hass.async_add_executor_job(_get_calendars)
-    components_results = await asyncio.gather(
-        *[
-            hass.async_add_executor_job(calendar.get_supported_components)
-            for calendar in calendars
+        return [
+            calendar
+            for calendar in client.principal().calendars()
+            if component in calendar.get_supported_components()
         ]
-    )
-    return [
-        calendar
-        for calendar, supported_components in zip(calendars, components_results)
-        if component in supported_components
-    ]
+
+    return await hass.async_add_executor_job(_get_calendars)
 
 
 def get_attr_value(obj: caldav.CalendarObjectResource, attribute: str) -> str | None: