Update pnpm to v8.15.9

Author: renovate[bot]

package.json

@@ -18,7 +18,7 @@
   },
   "volta": {
     "node": "18.18.2",
-    "pnpm": "8.14.1"
+    "pnpm": "8.15.9"
   },
   "pnpm": {
     "overrides": {

packages/fractal-page-object/package.json

@@ -68,7 +68,7 @@
   "dependencies": {
     "dom-element-descriptors": "^0.5.0"
   },
-  "packageManager": "pnpm@8.8.0",
+  "packageManager": "pnpm@8.15.9",
   "volta": {
     "extends": "../../package.json"
   }