Move vuex action helper spec to Jest

What does this MR do?

Adds the Vuex testAction spec to Jest. This also fixes a bug in the implementation, when run on Jest/node, whereby actions that returned rejected promises would always fail the given test.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Style guides
• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.