Bump @tiptap/extension-underline from 3.17.1 to 3.18.0

Bumps [@tiptap/extension-underline](https://github.com/ueberdosis/tiptap/tree/HEAD/packages/extension-underline) from 3.17.1 to 3.18.0.
- [Release notes](https://github.com/ueberdosis/tiptap/releases)
- [Changelog](https://github.com/ueberdosis/tiptap/blob/develop/packages/extension-underline/CHANGELOG.md)
- [Commits](https://github.com/ueberdosis/tiptap/commits/v3.18.0/packages/extension-underline)

---
updated-dependencies:
- dependency-name: "@tiptap/extension-underline"
  dependency-version: 3.18.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -23,7 +23,7 @@
         "@tiptap/extension-superscript": "^3.18.0",
         "@tiptap/extension-text-align": "^3.10.7",
         "@tiptap/extension-typography": "^3.10.7",
-        "@tiptap/extension-underline": "^3.10.7",
+        "@tiptap/extension-underline": "^3.18.0",
         "@tiptap/pm": "^3.10.7",
         "@tiptap/starter-kit": "^3.10.7",
         "tailwindcss": "^4.1.17"