chore(deps): update pnpm to v8.15.0

Author: renovate[bot]

package.json

@@ -4,7 +4,7 @@
   "private": false,
   "type": "module",
   "version": "2.0.0",
-  "packageManager": "pnpm@8.9.2",
+  "packageManager": "pnpm@8.15.0",
   "keywords": [
     "cssvars",
     "sass",