fix: the optional input language on the getAvailableVoices method

Author: Mhp23

src/NativeSpeech.ts

@@ -102,7 +102,7 @@ export interface Spec extends TurboModule {
   initialize: (options: VoiceOptions) => void;
   openVoiceDataInstaller: () => Promise<void>;
   setEngine: (engineName: string) => Promise<void>;
-  getAvailableVoices: (language: string) => Promise<VoiceProps[]>;
+  getAvailableVoices: (language?: string) => Promise<VoiceProps[]>;
   speakWithOptions: (text: string, options: VoiceOptions) => Promise<void>;
   //Listeners
   readonly onError: EventEmitter<EventProps>;

src/Speech.ts

@@ -26,7 +26,7 @@ export default class Speech {
    * const englishVoices = await Speech.getAvailableVoices('en');
    */
   public static getAvailableVoices(language?: string): Promise<VoiceProps[]> {
-    return TurboSpeech.getAvailableVoices(language ?? '');
+    return TurboSpeech.getAvailableVoices(language);
   }
   /**
    * Gets a list of all available text-to-speech engines on the device