Update compatibility testing-only dependencies (major) (#785)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package-lock.json

@@ -68,8 +68,8 @@
     "sass": "1.77.8",
     "simple-code-frame": "1.3.0",
     "smoldash": "0.11.0",
-    "svelte": "3.59.2",
-    "svelte-preprocess": "5.1.4",
+    "svelte": "4.2.18",
+    "svelte-preprocess": "6.0.2",
     "typescript": "5.5.4",
     "vue": "3.4.34"
   },