Allow verify markdown test with mdx parser

tests/config/format-test/verify-fixtures.js

@@ -138,7 +138,7 @@ const categoryParsers = new Map([
   ["lwc", { parsers: ["lwc"], verifyParsers: [], extensions: [".html"] }],
   [
     "markdown",
-    { parsers: ["markdown"], verifyParsers: [], extensions: [".md"] },
+    { parsers: ["markdown"], verifyParsers: ["mdx"], extensions: [".md"] },
   ],
   ["mdx", { parsers: ["mdx"], verifyParsers: [], extensions: [".mdx"] }],
   [