Migration changes shouldnt update vault

I've just been caught out with a small gotcha as it was not an expected behaviour.

Running supabase migrations push --linked also triggers an update to the vault settings.

I would not expect this to happen as we update the vault as part of our migrations using values injected from a .env file or as part of a db reset.

I would suggest this was an optional flag rather than a default behaviour, as it is not documented in the help documentation either.