Rollup merge of #153534 - Zalathar:flaky-stress, r=Mark-Simulacrum

Remove a flaky `got_timeout` assert from two channel tests

In CI, the receiver thread can be descheduled for a surprisingly long time, so there's no guarantee that a timeout actually occurs.

One of these tests actually failed in rust-lang/rust#153387 (comment).

Earlier failures:
- rust-lang/rust#150365 (comment)
- rust-lang/rust#147775 (comment)

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- Prior art: rust-lang/rust#152878

Author: JonathanBrouwer