Update pnpm to v8.15.9

Author: renovate[bot]

ember-modify-based-class-resource/package.json

@@ -114,7 +114,7 @@
     "main": "addon-main.cjs",
     "app-js": {}
   },
-  "packageManager": "pnpm@8.12.1",
+  "packageManager": "pnpm@8.15.9",
   "volta": {
     "extends": "../package.json"
   }

package.json

@@ -23,15 +23,15 @@
     "release-plan": "^0.6.0",
     "typescript": "^5.0.0"
   },
-  "packageManager": "pnpm@8.12.1",
+  "packageManager": "pnpm@8.15.9",
   "engines": {
     "node": ">= 18.*",
     "npm": "use pnpm",
     "yarn": "use pnpm"
   },
   "volta": {
     "node": "20.10.0",
-    "pnpm": "8.12.1"
+    "pnpm": "8.15.9"
   },
   "pnpm": {
     "overrides": {