Fix union validator to correctly identify inherited classes in discriminated unions #5671

Job	Run time
rust benchmarks	56s
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
build sdist	13s
build-wasm-emscripten	52s
coverage	1m 39s
lint	43s
test-debug 3.13	47s
test-debug pypy3.10	39s
test MSRV	48s
test on ubuntu	40s
test-pydantic-integration	39s
test on macos	52s
test on windows	2m 21s
test 3.9	41s
test 3.10	41s
test 3.11	39s
test 3.12	37s
test 3.13	41s
test 3.13t	42s
test pypy3.9	46s
test pypy3.10	44s
test build on ${{ matrix.os }}	0s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
inspect-pypi-assets	0s
check	2s
release	0s
	16m 42s

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