chore: more thorough markdown extension check

package.json

@@ -62,7 +62,7 @@
     "**/*.scss": [
       "npx prettier --write"
     ],
-    "**/*.{md,markdown}": [
+    "**/*.{md,mkd,mdwn,mdown,mdtxt,mdtext,markdown}": [
       "npx markdownlint --config ./markdownlint.config.json --fix"
     ]
   }