Fixes discriminated union bug regression when using enums #4569

Job	Run time
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
rust benchmarks	3m 50s
build sdist	15s
build-wasm-emscripten	3m 27s
coverage	3m 34s
lint	1m 37s
test-debug 3.11	1m 11s
test MSRV	3m 12s
test-debug pypy3.10	2m 3s
test on ubuntu	3m 26s
test-pydantic-integration	2m 5s
test 3.8	2m 46s
test on macos	3m 18s
test 3.9	2m 54s
test on windows	6m 22s
test 3.10	2m 57s
test 3.11	2m 56s
test 3.12	3m 2s
test pypy3.9	3m 13s
test pypy3.10	3m 29s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.os }}	0s
inspect-pypi-assets	0s
check	1s
release	0s
	55m 38s

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