What kind of change does this PR introduce?

If the browserslist config references an exported Browserslist like
extends @foo/browserslist-config with configs for two or more environments

module.exports = {
    production: [
        '>= 0.5%',
        'not Explorer <= 11'
    ],
    legacy: [
        '>= 1%',
        'Explorer >= 11'
    ]
}

the environment will not be respected if you set config.target like
config.target = 'browserslist:production'

Did you add tests for your changes?
No

Does this PR introduce a breaking change?
I don't think so

What needs to be documented once your changes are merged?

Nothing