message: fix(config): map build variants correctly
  In particular, map `darwin_codesign` to `darwin` because that
  influences the path where the release artifact ends up being put.
diff: @@ -50,6 +50,8 @@ const REVISION = process.env.IS_PATCH ?
  `pr-${process.env.GITHUB_PR_NUMBER}-${process.env.REVISION_ORDER_ID}` :
  process.env.REVISION;
  +const BUILD_VARIANT = (process.env.BUILD_VARIANT || '').split('_')[0];
  +
  /**
  * Export the configuration for the build.
  */
  @@ -73,7 +75,7 @@ module.exports = {
  isPatch: process.env.IS_PATCH === 'true',
  platform: os.platform(),
  execNodeVersion: process.env.NODE_JS_VERSION || `^${process.version.slice(1)}`,
  - buildVariant: process.env.BUILD_VARIANT,
  + buildVariant: BUILD_VARIANT,
  appleCodesignIdentity: process.env.APPLE_CODESIGN_IDENTITY,
  appleCodesignEntitlementsFile: path.resolve(__dirname, 'macos-entitlements.xml'),
  appleNotarizationBundleId: APPLE_NOTARIZATION_BUNDLE_ID,
  