[slang] Fix virtual interface comparison #1607

Job	Run time
bindings	19m 25s
conan	6m 53s
build (clang-sanitize, ubuntu-22.04)	34m 25s
linux-coverage	11m 55s
build (gcc-release, ubuntu-22.04)	8m 9s
build (gcc-11-release, ubuntu-22.04)	7m 50s
build (gcc-debug-shared, ubuntu-22.04)	7m 26s
build (gcc-debug-noexcept, ubuntu-22.04)	7m 22s
build (macos-release, macos-13)	5m 36s
build (win64-release, windows-latest)	11m 18s
build (win64-debug-shared, windows-latest)	9m 3s
build (win64-debug-noexcept, windows-latest)	7m 54s
	2h 17m 16s

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