FIX-#425: Fix type of shared MPI.buffer (#426) #862

Job	Run time
lint (black)	6s
lint (flake8)	6s
test-ubuntu (backend ray, python 3.9)	1m 55s
test-ubuntu (backend mpi, python 3.9)	1m 58s
test-ubuntu (backend dask, python 3.9)	2m 6s
test-ubuntu (backend pymp, python 3.9)	2m 3s
test-ubuntu (backend pyseq, python 3.9)	1m 54s
test-ubuntu (backend ray, python 3.10)	2m 7s
test-ubuntu (backend mpi, python 3.10)	2m 6s
test-ubuntu (backend dask, python 3.10)	1m 59s
test-ubuntu (backend pymp, python 3.10)	1m 44s
test-ubuntu (backend pyseq, python 3.10)	1m 41s
test-windows (backend ray, python 3.9)	5m 40s
test-windows (backend mpi, python 3.9)	6m 22s
test-windows (backend dask, python 3.9)	5m 56s
test-windows (backend pymp, python 3.9)	5m 5s
test-windows (backend pyseq, python 3.9)	5m 27s
test-windows (backend ray, python 3.10)	6m 7s
test-windows (backend mpi, python 3.10)	6m 19s
test-windows (backend dask, python 3.10)	5m 17s
test-windows (backend pymp, python 3.10)	5m 57s
test-windows (backend pyseq, python 3.10)	5m 57s
	1h 17m 52s

Provide feedback