Improve test.

tests/sanity/extra/extra-docs.json

@@ -1,7 +1,9 @@
 {
     "include_symlinks": false,
     "prefixes": [
-        "docs/docsite/"
+        "docs/docsite/",
+        "plugins/",
+        "roles/"
     ],
     "output": "path-line-column-message",
     "requirements": [

tests/sanity/extra/extra-docs.py

@@ -13,8 +13,6 @@ import subprocess
 
 def main():
     """Main entry point."""
-    if not os.path.isdir(os.path.join('docs', 'docsite')):
-        return
     p = subprocess.run(['antsibull-docs', 'lint-collection-docs', '--plugin-docs', '--disallow-semantic-markup', '--skip-rstcheck', '.'], check=False)
     if p.returncode not in (0, 3):
         print('{0}:0:0: unexpected return code {1}'.format(sys.argv[0], p.returncode))