Add accessibility label for "QR code" button in Audio sharing page.

Test: atest
Bug: 354112158
Flag: com.android.settingslib.flags.enable_le_audio_sharing
Change-Id: I5d2e2c70ca76e3598ca3d9550ebcc140d3400e34

tests/robotests/src/com/android/settings/connecteddevice/audiosharing/AudioSharingNamePreferenceTest.java

@@ -117,6 +117,7 @@ public class AudioSharingNamePreferenceTest {
         assertThat(shareButton.getVisibility()).isEqualTo(View.VISIBLE);
         assertThat(shareButton.getDrawable()).isNotNull();
         assertThat(shareButton.hasOnClickListeners()).isTrue();
+        assertThat(shareButton.getContentDescription()).isNotNull();
         assertThat(divider).isNotNull();
         assertThat(divider.getVisibility()).isEqualTo(View.VISIBLE);