[red-knot] fix non-callable reporting for unions (#16387) #41219

Job	Run time
cargo fmt	25s
cargo build (release)	6m 45s
Determine changes	12s
mkdocs	2m 36s
pre-commit	3m 54s
python package	1m 31s
cargo fuzz build	4m 6s
benchmarks	4m 25s
cargo clippy	1m 54s
cargo build (msrv)	2m 3s
cargo shear	23s
cargo test (linux)	2m 1s
cargo test (linux, release)	4m 3s
cargo test (wasm)	1m 38s
cargo test (windows)	5m 31s
formatter instabilities and black similarity	3m 23s
test scripts	1m 12s
test ruff-lsp	36s
fuzz parser	0s
ecosystem	0s
	46m 38s

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