syscall: TestGroupCleanupUserNamespace failure on linux-s390x-ibm [1.17 backport]

[gopherbot]

@bcmills requested issue #52088 to be considered for backport to the next 1.17 minor release.

@gopherbot, please backport to Go 1.17 and 1.18. This is a test-only fix for an issue exposed by a builder upgrade.

[gopherbot]

Change https://go.dev/cl/398235 mentions this issue: [release-branch.go1.17] syscall: relax output check in TestGroupCleanupUserNamespace

[gopherbot]

Closed by merging 2150be1 to release-branch.go1.17.