ci: increase max-parallel jobs to 8 in benchmarks workflow

Speed up benchmark execution by allowing more concurrent jobs.

Author: mattsu2020

.github/workflows/benchmarks.yml

@@ -26,7 +26,7 @@ jobs:
       CARGO_INCREMENTAL: 0
     strategy:
       fail-fast: false
-      max-parallel: 4
+      max-parallel: 8
       matrix:
         type: [simulation, memory]
         group: [text, file, numeric, misc]