Context

As part of WTBUILD-344 to increase the success rate of finding a stable wiredtiger commit and not failing auto-triggers, we need tasks in a few build variants to be scheduled to run more frequently to achieve the "75% tasks scheduled" stable commit selection criteria.

Current state:

• ubuntu2004-stress-tests: .cppsuite-stress-test (10 tasks) at batchtime:720 → 27/37 = 72.97% (BELOW threshold)
• ubuntu2004: .workgen-test (22 tasks) at batchtime:1440 → 102/130 = 78.5% (narrow margin)

Changes to test/evergreen.yml

• ubuntu2004-stress-tests: .cppsuite-stress-test batchtime 720 → 120 (every 2 hours)
• ubuntu2004: .workgen-test batchtime 1440 → 120 (every 2 hours)

Leave model-test-long* and csuite-long-running at batchtime:1440.