There's a really simple blunt way to do this wholesale. Set the "do not edit" property on all the steps in your workflow. That will prevent any edits and hide the button completely, while still letting you do all the workflow actions. It overrides the edit permission in the permission scheme.
You can see an example in the fixed default JIRA workflow - the property is set on the "closed" status. See https://confluence.atlassian.com/adminjiraserver071/workflow-properties-802592825.html for more
You can set it so that some groups can edit as well, but they will get the edit button back if they do that.
From the document Nic pointed, the following syntax will be helpful for your requirement:
some-group-one and some-group-two are the only group members to edit the issue. Add these permissions to all the statuses in your workflow.
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