ci: Change logs verification test to check for 'WARNING', not 'WARN'
ci: Change logs verification test to check for 'WARNING', not 'WARN'

Logrus warning logs are labeled 'WARNING [...' -- this test previously
checked for the incorrect string 'WARN [...', causing the test
to miss any warnings thrown by the minion.

LuiseV/quilt,NetSys/quilt,NetSys/quilt,NetSys/quilt,kelda/kelda,kelda/kelda,LuiseV/quilt,quilt/quilt,LuiseV/quilt,kelda/kelda,quilt/quilt,LuiseV/quilt,LuiseV/quilt,quilt/quilt,quilt/quilt,NetSys/quilt,kelda/kelda,NetSys/quilt