fixup! Bug 42562: Normalized the Accepted Languages on Android.

Bug 42582: Use toLanguageTag() instead of toString()

mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoRuntimeSettings.java

@@ -1076,7 +1076,7 @@ public final class GeckoRuntimeSettings extends RuntimeSettings {
         }
       }
     }
-    String acceptLanguages = locale != null ? locale.toString().replace('_', '-') : "en-US";
+    String acceptLanguages = locale != null ? locale.toLanguageTag().replace('_', '-') : "en-US";
     if (acceptLanguages.equals("en-US")) {
       // For consistency with spoof English.
       acceptLanguages += ", en";