Previously, `BootedStorage::new()` unconditionally tried to open
`/sysroot` before checking the environment type. This caused
`bootc status` to fail on non-ostree/composefs systems.
(We did work in containers and we had tests for that; but
the container case is special cased even earlier)
Fixes: https://issues.redhat.com/browse/RHEL-135687
Assisted-by: Claude Code (Opus 4.5)
Signed-off-by: Colin Walters <walters@verbum.org>
