Workaround #3072
Workaround #3072

This forces the two GIL reacquire tests to run serially as the
concurrent application of ctypes callbacks causes segfaults.

stuartarchibald/numba,jriehl/numba,stuartarchibald/numba,IntelLabs/numba,stuartarchibald/numba,cpcloud/numba,sklam/numba,gmarkall/numba,IntelLabs/numba,IntelLabs/numba,seibert/numba,numba/numba,jriehl/numba,numba/numba,gmarkall/numba,stonebig/numba,gmarkall/numba,jriehl/numba,gmarkall/numba,numba/numba,cpcloud/numba,cpcloud/numba,IntelLabs/numba,gmarkall/numba,stonebig/numba,stonebig/numba,seibert/numba,numba/numba,stonebig/numba,sklam/numba,IntelLabs/numba,sklam/numba,stonebig/numba,seibert/numba,numba/numba,jriehl/numba,seibert/numba,stuartarchibald/numba,sklam/numba,stuartarchibald/numba,cpcloud/numba,sklam/numba,cpcloud/numba,jriehl/numba,seibert/numba