pw-apply: Fix timezone parsing in the new patch age warning

Prevent re-splitting of strings. Otherwise when patchwork gives
us "2023-11-18T18:01:55 UTC" we'll miss the timezone.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Paolo Abeni <pabeni@redhat.com>