lint only some variable types

stylelint.config.js

const variables = require('stylelint-config-primer/plugins/variables')
const {DEFAULT_RULES} = variables

const variableRules = {}
for (const rule of Object.keys(DEFAULT_RULES)) {
  variableRules[rule] = false
}

module.exports = {
  plugins: [variables],
  rules: {
    'primer/variables': [true, Object.assign(variableRules, {
      margin: DEFAULT_RULES.margin,
      padding: DEFAULT_RULES.padding
    }]
  }
}