[mixer] Use register_apply_action for mixer_speaker.apply_ducking (#19689)

tests/components/mixer/common-actions.yaml

@@ -0,0 +1,8 @@
+button:
+  - platform: template
+    name: Duck media
+    on_press:
+      - mixer_speaker.apply_ducking:
+          id: source_speaker_1_id
+          decibel_reduction: !lambda return 20;
+          duration: !lambda return 250;

tests/components/mixer/test-actions.esp32-idf.yaml

@@ -0,0 +1,8 @@
+substitutions:
+  dout_pin: GPIO14
+
+packages:
+  spi: !include ../../test_build_components/common/spi/esp32-idf.yaml
+  i2s_audio: !include ../../test_build_components/common/i2s_audio/esp32-idf.yaml
+  mixer: !include common.yaml
+  actions: !include common-actions.yaml