refactor(tests): reduce shard count from 8 to 6 for parallel testing

.github/workflows/insomnia-test.yml

@@ -102,8 +102,8 @@ jobs:
       fail-fast: false
       matrix:
         # To scale up, add indices here and bump shardTotal to match.
-        shardIndex: [1, 2, 3, 4, 5, 6, 7, 8]
-        shardTotal: [8]
+        shardIndex: [1, 2, 3, 4, 5, 6]
+        shardTotal: [6]
     steps:
       - name: Checkout repo
         uses: actions/checkout@fbc6f3992d24b796d5a048ff273f7fcc4a7b6c09 # v5