Simple switch timer v2: Mark dp 38 optional in available check.

The check is against null, but the dp was not marked optional, as it
was in the original location.

Update unit test to check the available logic correctly for this file.

custom_components/tuya_local/devices/simple_switch_timerv2.yaml

@@ -49,6 +49,7 @@ secondary_entities:
       - id: 38
         type: string
         name: available
+        optional: true
         mapping:
           - dps_val: null
             value: false

tests/devices/test_simple_switch_with_timerv2.py

@@ -9,6 +9,7 @@
 
 SWITCH_DPS = "1"
 TIMER_DPS = "9"
+INITIAL_STATE_DPS = "38"
 
 
 class TestTimedSwitch(BasicNumberTests, SwitchableTests, TuyaDeviceTestCase):
@@ -32,3 +33,11 @@ def test_extra_state_attributes_set(self):
             self.subject.extra_state_attributes,
             {},
         )
+
+    def test_available(self):
+        for id, e in self.entities.items():
+            if id == "select_initial_state":
+                self.dps[INITIAL_STATE_DPS] = None
+                self.assertFalse(e.available)
+                self.dps[INITIAL_STATE_DPS] = "on"
+            self.assertTrue(e.available)