test: Do not assume threaded completion order (#62795)
The `Threads.foreach(f, ::Channel)` testset in `test/threads_exec.jl`
asserts that with `ntasks=10` the results come back in a different order
from the input (`@test expected != unordered_fair` / `!=
unordered_static`). That is a statement about scheduling luck, not
`Threads.foreach` semantics: nothing guarantees that multiple tasks
complete items out of order.
The retry of the coverage PR's [x86_64-linux-gnuassertrr
job](https://buildkite.com/julialang/julia-pr/builds/1472#01a00201-1630-466d-b4ad-8f2cb0ce31e5)
failed in the `JULIA_NUM_THREADS=1,1` pass when the fair schedule
happened to preserve input order:
```
Test Failed at test/threads_exec.jl:1139
Expression: expected != unordered_fair
```
Remove the two scheduling-sensitive checks. The single-worker ordering
checks (`ntasks=1` must preserve order) and multiset-equality checks
remain.
Assisted by: Fable & Sol
Co-authored-by: OpenAI Codex <noreply@openai.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
