TestNewApp_StopTimeout and TestNewApp_SendsFxEventsToTheLogger both
build the app graph, which runs config.New, so a variable exported in
the developer's shell reached them: METRICS_USERNAME without
METRICS_PASSWORD failed the second. Both now call
config.ClearEnvForTest before setting their own variables, as the
config tests and the gormlog first-boot test already do.
Model: opus-5-5