chore: mark scan command for removal in 2026.9.1+1

[oz123]

The command is marked as deprecated for quite a while now, with no explicit target for removal.

    p.add_argument(
        "--scan",
        dest="scan",
        action="store_true",
        default=False,
        help="Use the new scan command instead of the deprecated check command.",
    )

I hereby suggest to make a release which marks the removal with a date and do a release after this date
which removes this feature.
The next release we do, should have an explicit note:

help="Use the new scan command instead of the deprecated check command (removal in the version that follows:  v2026.9.1."