[PATCH 5.15.y] selftests: arm64: signal: skip SVE VL change test with single VL

[Sasha Levin]

> [PATCH 5.15.y] selftests: arm64: signal: skip SVE VL change test with single VL

Can we keep the commit message the same as upstream? Is there a reason to
rewrite it?

-- 
Thanks,
Sasha