fix(test): use parsers.get not parsers.has to detect erlang WASM availability

parsers.has('erlang') returns true even when WASM loading fails because
doLoadLanguage sets the key to null on error. Use !!parsers.get('erlang')
so the suite skips correctly when the grammar is absent.

Author: carlos-alm

tests/parsers/erlang.test.ts

@@ -9,7 +9,7 @@ describe('Erlang parser', () => {
 
   beforeAll(async () => {
     parsers = await createParsers();
-    erlangAvailable = parsers.has('erlang');
+    erlangAvailable = !!parsers.get('erlang');
   });
 
   function parseErlang(code) {