fix format option in tutorial_variational_classifier (#1566)

## Summary

This PR adds a missing colon (:) to the `format` role option in the
`html` role definition, fixing anchor tag rendering issues in the
`tutorial_variational_classifier` demo.

Author: jontoye

demonstrations_v2/tutorial_variational_classifier/demo.py

@@ -1,6 +1,6 @@
 r"""
 .. role:: html(raw)
-    format: html
+    :format: html
 
 .. _variational_classifier:
 

demonstrations_v2/tutorial_variational_classifier/metadata.json

@@ -8,7 +8,7 @@
     "executable_stable": true,
     "executable_latest": true,
     "dateOfPublication": "2019-10-11T00:00:00+00:00",
-    "dateOfLastModification": "2025-09-22T15:48:14+00:00",
+    "dateOfLastModification": "2025-10-03T15:48:14+00:00",
     "categories": [
         "Quantum Machine Learning",
         "Getting Started"