Rename en-GB language to en (#2866)

Fixes https://github.com/element-hq/element-call/issues/2865

If we want to have GB and US specific terms later on we can then add then in as `en-GB` and `en-US`.

src/TranslatedError.ts

@@ -22,7 +22,7 @@ export abstract class TranslatedError extends Error {
     messageKey: ParseKeys<DefaultNamespace, TOptions>,
     translationFn: TFunction<DefaultNamespace>,
   ) {
-    super(translationFn(messageKey, { lng: "en-GB" } as TOptions));
+    super(translationFn(messageKey, { lng: "en" } as TOptions));
     this.translatedMessage = translationFn(messageKey);
   }
 }