Use ?? instead of || (#3299)

* Use ?? instead of ||

* Fix $ in front of feature flag

Author: Llorenç Muntaner

src/frontend/src/lib/components/wizards/auth/views/PickAuthenticationMethod.svelte

@@ -58,8 +58,8 @@
 
   const supportsPasskeys = nonNullish(window.PublicKeyCredential);
   const showGoogleButton =
-    canisterConfig.openid_google?.[0]?.[0] && !ENABLE_GENERIC_OPEN_ID;
-  const openIdProviders = canisterConfig.openid_configs?.[0] || [];
+    canisterConfig.openid_google?.[0]?.[0] && !$ENABLE_GENERIC_OPEN_ID;
+  const openIdProviders = canisterConfig.openid_configs?.[0] ?? [];
 </script>
 
 <div class="flex flex-col items-stretch gap-6">