Add <9.12.0 to .engines.pnpm (#39897)

We're waiting on updating to pnpm 9.12+ due to the regression of
pnpm/pnpm#3935. Update `.engines.pnpm` so Renovate stops trying to use
9.12 and then failing the "Lock files are up to date" check.

package.json

@@ -35,6 +35,6 @@
 	},
 	"engines": {
 		"node": "^22.9.0",
-		"pnpm": "^9.3.0"
+		"pnpm": "^9.3.0 <9.12.0"
 	}
 }