Resolve `redundantAssignment` in `pkcs1_decode` #984

Job	Run time
build_python_27 (ubuntu-20.04, yes)	2m 33s
mypy	13s
build_python_27 (ubuntu-20.04, no)	2m 37s
build (3.6, yes, ubuntu-20.04)	2m 32s
build_python_27 (windows-latest, yes)	4m 0s
build (3.6, no, ubuntu-20.04)	2m 24s
build_python_27 (windows-latest, no)	3m 47s
build (3.7, yes, ubuntu-20.04)	2m 35s
python_no_gil	2m 56s
build (3.7, no, ubuntu-20.04)	2m 27s
build (3.8, yes, ubuntu-20.04)	2m 15s
test_c_windows (x64)	45s
test_c_windows (win32)	1m 3s
build (3.8, no, ubuntu-20.04)	2m 17s
build (3.9, yes, ubuntu-20.04)	2m 19s
build (3.9, no, ubuntu-20.04)	2m 16s
build (3.10, yes, ubuntu-20.04)	2m 15s
build (3.10, no, ubuntu-20.04)	2m 13s
build (3.11, yes, ubuntu-20.04)	1m 51s
build (3.11, no, ubuntu-20.04)	1m 56s
build (3.12, yes, ubuntu-20.04)	1m 59s
test_c_linux (0, x64)	52s
build (3.12, no, ubuntu-20.04)	2m 15s
test_c_linux (0, x32)	1m 0s
build (3.13-dev, yes, ubuntu-20.04)	2m 10s
test_c_linux (1, x64)	54s
build (3.13-dev, no, ubuntu-20.04)	2m 21s
test_c_linux (1, x32)	1m 6s
build (3.12, yes, macos-12)	3m 52s
build (3.12, no, windows-latest)	3m 52s
build (3.12, yes, windows-latest)	4m 9s
build (pypy2.7, no, ubuntu-latest)	1m 30s
build (pypy3.9, no, ubuntu-latest)	1m 38s
	1h 12m 52s

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