test: warning behaviour for unset/set TARGETOS,TARGETARCH,TARGETPLATFORM
test: warning behaviour for unset/set TARGETOS,TARGETARCH,TARGETPLATFORM

Test buildah's warning behavious for unset or set TARGETOS, TARGETARCH,
TARGETPLATFORM or TARGETVARIANT args when set or unset directly or
indirectly by the user.

Adds missing test for: https://github.com/containers/buildah/pull/4295

Co-authored-by: Ed Santiago <792d28329de7ed446c01b83f731a071248ffeaf4@redhat.com>
Signed-off-by: Aditya R <4f9683854fe0b71db89677d592545c6b565c2266@redhat.com>

nalind/buildah-1,nalind/buildah-1,TomSweeneyRedHat/buildah,TomSweeneyRedHat/buildah,nalind/buildah-1,TomSweeneyRedHat/buildah