cmd/dist: enable race detector test on S390X
cmd/dist: enable race detector test on S390X

The support was added but the test was not enabled. Enable it.

Fixes #53981.

Change-Id: I81ea73ea4ebc1013c35cb70ae88b096e02497887
Reviewed-on: https://go-review.googlesource.com/c/go/+/418914
Run-TryBot: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

nawawi/go,nawawi/go,nawawi/go,golang/go,golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go,golang/go,golang/go,nawawi/go,golang/go,golang/go,golang/go,nawawi/go