A random failure in WorkflowJobNonRestartingTest.missingContextCheck turned up a problem.
When throwing MissingContextVariableException, we have no way of knowing which type is actually supplied.
If we happen to pick Launcher (this is random!), ExecutorStep will not be mentioned in the error.
Provisionally working around this reverting commit 4ac760a1f9c76f6bfd9a1005db133a4e7de6ab9a
so that ExecutorStep is considered to also supply Launcher (and Node).