Make `jl_*affinity` tests more portable (#55261)
Changes made:
- Use 0 for the thread ID to ensure it's always valid. The function
expects `0 <= tid < jl_n_threads` so 1 is incorrect if `jl_n_threads` is
1.
- After retrieving the affinity mask with `jl_getaffinity`, pass that
same mask back to `jl_setaffinity`. This ensures that the mask is always
valid. Using a mask of all ones results in `EINVAL` on FreeBSD. Based on
the discussion in #53402, this change may also fix Windows, so I've
tried reenabling it here.
- To check whether `jl_getaffinity` actually did something, we can check
that the mask is no longer all zeros after the call.
Fixes #54817
