Fixing `exclude_none` for json serialization of `computed_field`s #4023

Job	Run time
test on ubuntu	2m 41s
test 3.7	2m 24s
test on macos	4m 12s
coverage	3m 34s
test 3.8	2m 17s
test on windows	5m 22s
test 3.9	2m 27s
test 3.10	2m 20s
test 3.11	2m 32s
test-debug 3.11	1m 18s
test-debug pypy3.10	1m 52s
test 3.12	2m 23s
rust benchmarks	3m 39s
test pypy3.7	2m 49s
test pypy3.8	2m 38s
test pypy3.9	2m 44s
lint	1m 20s
test pypy3.10	2m 54s
test-pydantic-integration	1m 43s
build sdist	14s
build-wasm-emscripten	2m 51s
build on ${{ matrix.os }} (${{ matrix.target }} - ${{ matrix.interpreter \|\| 'all' }}${{ (((matrix.os == 'linux') && format(' - {0}', (((matrix.manylinux == 'auto') && 'manylinux') \|\| matrix.manylinux))) \|\| '') }})	0s
build pgo-optimized on ${{ matrix.os }} / ${{ matrix.interpreter }}	0s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.os }}	0s
inspect-pypi-assets	0s
check	2s
release	0s
	54m 16s

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