fix(test): increase CI harness frequency before Release (#8343)

## Problem
Capture errors around acl, multi tenancy, minio side

## Solution
Increase run frequency as a safe guard

Author: skrdgraph

.github/workflows/ci-dgraph-load-tests.yml

@@ -7,7 +7,7 @@ on:
     branches:
       - main
   schedule:
-    - cron: "*/30 * * * *"
+    - cron: "*/15 * * * *"
 jobs:
   dgraph-load-tests:
     runs-on: self-hosted

.github/workflows/ci-dgraph-tests.yml

@@ -7,7 +7,7 @@ on:
     branches:
       - main
   schedule:
-    - cron: "*/30 * * * *"
+    - cron: "*/15 * * * *"
 jobs:
   dgraph-tests:
     runs-on: self-hosted