ci: increase parallelism for Linux E2E

This reduced the Linux CI time by around 7 mins

(cherry picked from commit 0600c77)

Author: alan-agius4

.circleci/config.yml

@@ -198,7 +198,7 @@ jobs:
     executor:
       name: test-executor
       nodeversion: << parameters.nodeversion >>
-    parallelism: 6
+    parallelism: 8
     steps:
       - custom_attach_workspace
       - browser-tools/install-chrome