Bug description
calling unregisterStepsFromJob and getStep from two Threads in parallel can lead to a NullPointerException

Environment
Spring Batch Version 5.2.3
All Jdk Versions, I tried jdk 17 and 21

Steps to reproduce
Here is an example which can lead to this race condition:

StepRegistry registry = new MapStepRegistry();
registry.register("foo", List.of(new TaskletStep("first")));
Thread first = new Thread() {
	@Override
	public void run() {
		registry.unregisterStepsFromJob("foo");
	}
};
first.start();
try {
	registry.getStep("foo", "first");
}
catch (NoSuchJobException e) {
}

Expected behavior
getStep should either return the Step or throw a NoSuchJobException.

Minimal Complete Reproducible example
Failing Tests

I used vmlens to make the test execute all thread interlreavings and make the test reproducible