Bump version to `v2.31.1` #5777

Job	Run time
rust benchmarks	2m 44s
build pgo-optimized on ${{ matrix.os }} / ${{ matrix.interpreter }}	0s
build on ${{ matrix.os }} (${{ matrix.target }} - ${{ matrix.interpreter \|\| 'all' }}${{ (((matrix.os == 'linux') && format(' - {0}', (((matrix.manylinux == 'auto') && 'manylinux') \|\| matrix.manylinux))) \|\| '') }})	0s
build sdist	21s
coverage	2m 7s
build-wasm-emscripten	2m 35s
lint	48s
test-debug 3.13	55s
test MSRV	2m 37s
test-debug pypy3.10	3m 14s
test on ubuntu	2m 1s
test on macos	2m 48s
test-pydantic-integration	1m 12s
test on windows	6m 11s
test 3.9	1m 57s
test 3.10	1m 59s
test 3.11	1m 49s
test 3.12	1m 59s
test 3.13	1m 47s
test 3.13t	2m 6s
test pypy3.9	4m 17s
test pypy3.10	3m 59s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.os }}	0s
inspect-pypi-assets	0s
check	2s
release	0s
	47m 28s

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