ci(NODE-6752): unskip flaky SCRAM auth tests

[baileympearson]

Description

What is changing?

Unskips and fixes the flaky auth tests. The problem appears to be the use of Promise.all() instead of Promise.allSettled() when creating multiple users concurrently. Promise.all() meant that sometimes, by the time the tests started running, only some of the required test users had been created.

I ran a patch across all our variants that run these tests, each variant running the tests 1000 times: https://spruce.mongodb.com/version/6862c34402854f00079a3f3a/tasks?page=0&sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC. The only failures are on Windows replica set 4.2. I'm not sure why these failed, but I fixed those failures by creating users in a before, instead of a beforeEach.

Is there new documentation needed for these changes?

What is the motivation for this change?

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