fix(workflow): enable workflow per method (#1569)

Workflow needs to be enabled per method. `persistEntry` should only use it when persisting an unpublished entry, but must behave as if workflow were not enabled for publishing. This fixes a 2.0 regression.

packages/netlify-cms-backend-github/src/implementation.js

@@ -43,7 +43,6 @@ export default class GitHub {
       repo: this.repo,
       api_root: this.api_root,
       squash_merges: this.squash_merges,
-      useWorkflow: this.options.useWorkflow,
       initialWorkflowStatus: this.options.initialWorkflowStatus,
     });
     return this.api.user().then(user =>