`tailscale set` was created to set preferences, which used to be
overloaded into `tailscale up`. To move people over to the new
command, `up` was supposed to be frozen and no new preference flags
would be added. But people forgot, there was no test to warn them, and
so new flags were added anyway.
TestUpFlagSetIsFrozen complains when new flags are added to
`tailscale up`. It doesn’t try all combinations of GOOS, but since
the CI builds in every OS, the pull-request tests should cover this.
Updates #15460
Signed-off-by: Simon Law <sfllaw@sfllaw.ca>
Simon Law
7e296923ab