Bump version for 4.2.0 release (#843) #1306

Job	Run time
Python 3.7 on macos-13	1m 6s
py312 on alpine	1m 4s
Python 3.12 on macos-13	52s
Python 3.7 on win32	8m 28s
py312 on alpine:aarch64	1m 16s
Python 3.12 on macos-latest	33s
pep8,packaging on linux, Rust stable	1m 2s
Python 3.12 on win32	2m 14s
py312 on ubuntu-rolling:aarch64	1m 8s
mypy on linux, Rust stable	35s
Python 3.7 on win64	1m 25s
py37 on linux, Rust stable	47s
Python 3.12 on win64	1m 24s
py38 on linux, Rust stable	38s
py39 on linux, Rust stable	31s
py310 on linux, Rust stable	36s
py311 on linux, Rust stable	37s
py312 on linux, Rust stable	38s
py313 on linux, Rust stable	43s
pypy3 on linux, Rust stable	50s
pypy3 on linux, Rust stable	52s
py312 on linux, Rust 1.64.0	2m 26s
py312 on linux, Rust beta	39s
py312 on linux, Rust nightly	40s
all-green	1s
	31m 5s

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