Remove support for Python 3.5 #862

Job	Run time
mypy	18s
build_python_27 (ubuntu-20.04, yes)	2m 25s
test_c_linux (0, x64)	1m 0s
build_python_27 (ubuntu-20.04, no)	2m 18s
build (3.6, yes, ubuntu-20.04)	2m 22s
test_c_linux (0, x32)	1m 0s
build_python_27 (windows-latest, yes)	4m 10s
test_c_windows (x64)	41s
test_c_linux (1, x64)	56s
build (3.6, no, ubuntu-20.04)	2m 17s
build_python_27 (windows-latest, no)	3m 53s
test_c_windows (win32)	1m 31s
test_c_linux (1, x32)	1m 2s
build (3.7, yes, ubuntu-20.04)	2m 10s
build (3.7, no, ubuntu-20.04)	2m 18s
build (3.8, yes, ubuntu-20.04)	2m 9s
build (3.8, no, ubuntu-20.04)	2m 6s
build (3.9, yes, ubuntu-20.04)	2m 4s
build (3.9, no, ubuntu-20.04)	2m 8s
build (3.10, yes, ubuntu-20.04)	2m 0s
build (3.10, no, ubuntu-20.04)	2m 15s
build (3.11, yes, ubuntu-20.04)	1m 51s
build (3.11, no, ubuntu-20.04)	1m 53s
build (3.12, yes, ubuntu-20.04)	1m 48s
build (3.12, no, ubuntu-20.04)	1m 53s
build (3.12, yes, macos-12)	2m 50s
build (3.12, no, windows-latest)	4m 7s
build (3.12, yes, windows-latest)	4m 26s
build (pypy2.7, no, ubuntu-latest)	1m 22s
build (pypy3.9, no, ubuntu-latest)	1m 33s
	1h 2m 46s

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