Bump next from 15.5.2 to 15.5.7 in /packages/theme

Bumps [next](https://github.com/vercel/next.js) from 15.5.2 to 15.5.7.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.5.2...v15.5.7)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 15.5.7
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

packages/theme/package.json

@@ -51,7 +51,7 @@
     "@vitest/ui": "^3.2.4",
     "clsx": "2.1.1",
     "jsdom": "^26.0.1",
-    "next": "15.5.2",
+    "next": "15.5.7",
     "styled-components": "5.3.11",
     "vitest": "^3.2.4"
   },