Not failing when Yarn lockfile is out of date

[gpoole]

Testing in v0.24.6 I noticed Yarn's stopped warning or failing if the lockfile is out of date, even with --frozen-lockfile: yarnpkg/yarn#3313.

The --frozen-lockfile flag seems to have broken in a couple of recent releases (yarnpkg/yarn#2538) and in v0.23.3 it was warning but still generating a new lockfile and exiting normally.

[SamVerschueren]

Nothing we can do about it as it's a Yarn issue