Fix concatenation of memoryviews in Python 2 #733

Job	Run time
mypy	22s
build_python_27 (ubuntu-20.04, yes)	3m 18s
build_python_27 (ubuntu-20.04, no)	3m 13s
build_python_27 (windows-latest, yes)	4m 17s
build_python_27 (windows-latest, no)	3m 40s
test_c_windows (x64)	1m 6s
test_c_windows (win32)	1m 10s
build (3.5, yes, ubuntu-20.04)	3m 15s
build (3.5, no, ubuntu-20.04)	3m 7s
build (3.6, yes, ubuntu-20.04)	3m 5s
build (3.6, no, ubuntu-20.04)	2m 36s
build (3.7, yes, ubuntu-20.04)	3m 9s
build (3.7, no, ubuntu-20.04)	2m 37s
build (3.8, yes, ubuntu-20.04)	2m 23s
build (3.8, no, ubuntu-20.04)	2m 42s
build (3.9, yes, ubuntu-20.04)	2m 54s
build (3.9, no, ubuntu-20.04)	2m 30s
build (3.10, yes, ubuntu-20.04)	2m 59s
build (3.10, no, ubuntu-20.04)	2m 37s
build (3.11, yes, ubuntu-20.04)	2m 13s
build (3.11, no, ubuntu-20.04)	2m 29s
build (3.11, yes, macos-12)	3m 49s
build (3.11, no, windows-latest)	4m 8s
build (3.11, yes, windows-latest)	4m 3s
build (pypy2.7, no, ubuntu-latest)	1m 58s
build (pypy3.8, no, ubuntu-latest)	2m 8s
test_c_linux (0, x64)	1m 13s
test_c_linux (0, x32)	1m 38s
test_c_linux (1, x64)	1m 20s
test_c_linux (1, x32)	1m 47s
	1h 17m 46s

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