Bump storybook from 8.6.14 to 8.6.15 (#7728)

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

packages/volto/package.json

@@ -379,7 +379,7 @@
     "release-it": "^19.0.5",
     "semver": "^7.5.4",
     "start-server-and-test": "1.14.0",
-    "storybook": "^8.0.4",
+    "storybook": "^8.6.15",
     "style-loader": "3.3.1",
     "stylelint": "^16.3.1",
     "stylelint-config-idiomatic-order": "10.0.0",