prettier: Disable for markdown files (#12333)

This is causing more pain than it is worth, especially since the prettier check currently only runs in the frontend test suite, so if a backend pull request introduces a new markdown file the CI will fail on some future run instead of on the PR. Sure, we can fix that, but is it worth the complexity? IMHO no.

Author: Turbo87

package.json

@@ -22,8 +22,8 @@
     "lint:hbs": "ember-template-lint app",
     "lint:js": "eslint . --cache",
     "precompress": "node ./script/precompress-assets.mjs",
-    "prettier:check": "prettier --check package.json '**/*.js' '**/*.mjs' '**/*.ts' '**/*.md'",
-    "prettier:write": "prettier --write package.json '**/*.js' '**/*.mjs' '**/*.ts' '**/*.md'",
+    "prettier:check": "prettier --check package.json '**/*.js' '**/*.mjs' '**/*.ts'",
+    "prettier:write": "prettier --write package.json '**/*.js' '**/*.mjs' '**/*.ts'",
     "start": "ember serve",
     "start:docker": "ember serve --proxy http://backend:8888",
     "start:live": "ember serve --proxy https://crates.io",