Update pnpm to v11.15.1 (#572)

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

Author: renovate[bot]

package.json

@@ -87,7 +87,7 @@
         "test": "gscan .",
         "zip": "gulp zip"
     },
-    "packageManager": "pnpm@11.15.0",
+    "packageManager": "pnpm@11.15.1",
     "devDependencies": {
         "@tryghost/shared-theme-assets": "2.7.1",
         "@tryghost/theme-translations": "^0.0.9",