Bump pnpm.

Author: iclanton

rush.json

@@ -26,7 +26,7 @@
    * Specify one of: "pnpmVersion", "npmVersion", or "yarnVersion".  See the Rush documentation
    * for details about these alternatives.
    */
-  "pnpmVersion": "8.7.6",
+  "pnpmVersion": "8.15.8",
 
   // "npmVersion": "6.14.15",
   // "yarnVersion": "1.9.4",