Fix union validator to correctly identify inherited classes in discriminated unions #5600

Job	Run time
rust benchmarks	52s
rust benchmarks	30s
build pgo-optimized on ${{ matrix.os }} / ${{ matrix.interpreter }}	0s
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 on ${{ matrix.os }} (${{ matrix.target }} - ${{ matrix.interpreter \|\| 'all' }}${{ (((matrix.os == 'linux') && format(' - {0}', (((matrix.manylinux == 'auto') && 'manylinux') \|\| matrix.manylinux))) \|\| '') }})	0s
build sdist	1m 2s
build sdist	15s
build-wasm-emscripten	1m 21s
build-wasm-emscripten	47s
coverage	1m 53s
coverage	32s
lint	1m 29s
lint	25s
test-debug 3.13	16s
test-debug 3.13	28s
test MSRV	39s
test MSRV	35s
test-debug pypy3.10	1m 3s
test-debug pypy3.10	26s
test on ubuntu	37s
test on ubuntu	27s
test-pydantic-integration	55s
test-pydantic-integration	41s
test on macos	1m 5s
test on macos	32s
test on windows	3m 41s
test on windows	1m 10s
test 3.9	49s
test 3.9	25s
test 3.10	1m 1s
test 3.10	38s
test 3.11	1m 15s
test 3.11	25s
test 3.12	50s
test 3.12	22s
test 3.13	1m 30s
test 3.13	24s
test pypy3.9	40s
test pypy3.9	28s
test pypy3.10	1m 14s
test pypy3.10	27s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.os }}	0s
test build on ${{ matrix.os }}	0s
inspect-pypi-assets	0s
inspect-pypi-assets	0s
check	3s
check	2s
release	0s
release	0s
	32m 14s

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