Resolve `redundantAssignment` in `pkcs1_decode` #1006

Job	Run time
mypy	17s
build_python_27 (ubuntu-20.04, yes)	2m 46s
build (3.6, yes, ubuntu-20.04)	2m 43s
build_python_27 (ubuntu-20.04, no)	2m 43s
python_no_gil	3m 0s
build_python_27 (windows-latest, yes)	3m 42s
build (3.6, no, ubuntu-20.04)	2m 37s
build_python_27 (windows-latest, no)	3m 43s
build (3.7, yes, ubuntu-20.04)	2m 40s
build (3.7, no, ubuntu-20.04)	2m 31s
test_c_linux (0, x64)	52s
test_c_linux (0, x32)	1m 2s
build (3.8, yes, ubuntu-20.04)	2m 21s
test_c_windows (x64)	54s
build (3.8, no, ubuntu-20.04)	2m 25s
test_c_linux (1, x64)	51s
test_c_windows (win32)	1m 4s
build (3.9, yes, ubuntu-20.04)	2m 26s
test_c_linux (1, x32)	1m 13s
build (3.9, no, ubuntu-20.04)	2m 21s
build (3.10, yes, ubuntu-20.04)	2m 20s
build (3.10, no, ubuntu-20.04)	2m 30s
build (3.11, yes, ubuntu-20.04)	2m 1s
build (3.11, no, ubuntu-20.04)	2m 7s
build (3.12, yes, ubuntu-20.04)	2m 2s
build (3.12, no, ubuntu-20.04)	2m 18s
build (3.13-dev, yes, ubuntu-20.04)	2m 3s
build (3.13-dev, no, ubuntu-20.04)	2m 31s
build (3.12, yes, macos-12)	3m 9s
build (3.12, no, windows-latest)	4m 17s
build (3.12, yes, windows-latest)	4m 34s
build (pypy2.7, no, ubuntu-latest)	1m 33s
build (pypy3.9, no, ubuntu-latest)	1m 43s
	1h 15m 19s

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