reduce dashboard_workers from 6 to 5 on circle

[davidsbailey]

No description provided.

[davidsbailey]

The goal of this PR is to avoid out of memory errors when running UI tests. example failure:

• circle/41221, memory-usage.txt

Decrementing the number of workers should save almost 1GB out of 8GB per container during UI tests.

Performance measurements

There has been some suspicion that decreasing the number of dashboard workers could substantially reduce UI test performance, however recent analysis suggests this is unfounded.

The run_ui_tests step took 1:08:10 on this PR: https://circleci.com/gh/code-dot-org/code-dot-org/41255#tests/containers/1 . The times for the same step on the past 5 successful staging builds took: [1:06:30, 1:11:18, 1:09:38, 1:07:12, 1:01:46] (average: 1:07:17).

Though this could represent a 1-minute slowdown, it seems within the noise margin so I'd propose we go ahead with this change and look at how UI test performance is affected over the course of the week.

[islemaster]

👍