atomic Unit tests for Dec and Inc not check edge cases

[psychocoderHPC]

The unit test for atomicDec is not testing the flip around based on the values.

https://github.com/alpaka-group/alpaka/blob/0b96515b1c8a24d0c3a2904081bc301311503770/include/alpaka/atomic/Op.hpp#L131

Some for atomicInc

https://github.com/alpaka-group/alpaka/blob/0b96515b1c8a24d0c3a2904081bc301311503770/include/alpaka/atomic/Op.hpp#L115

We simply test if an value is incremented or decremented:

https://github.com/alpaka-group/alpaka/blob/0b96515b1c8a24d0c3a2904081bc301311503770/test/unit/atomic/src/AtomicTest.cpp#L143-L185