[mormot] Adjust async (pinned) thread pool size for best results (#8293)

Co-authored-by: pavel.mash <[email protected]>

frameworks/Pascal/mormot/src/raw.pas

@@ -718,7 +718,7 @@ begin
     begin
       // asynchronus test
       servers := cpuCount;
-      threads := 4;
+      threads := 8;
     end
     else
     if GetEnvironmentVariable('TFB_TEST_NAME') = 'mormot-postgres-async2' then