[`pyupgrade`] Remove unreachable code in `UP015` implementation #37046

Job	Run time
cargo build (release)	0s
cargo fmt	20s
Determine changes	10s
mkdocs	2m 28s
pre-commit	38s
python package	1m 15s
benchmarks	4m 49s
cargo clippy	1m 46s
cargo build (msrv)	4m 7s
cargo fuzz build	0s
cargo shear	58s
cargo test (linux)	1m 43s
cargo test (wasm)	1m 32s
cargo test (linux, release)	3m 33s
cargo test (windows)	5m 12s
test scripts	57s
formatter instabilities and black similarity	0s
test ruff-lsp	36s
ecosystem	2m 33s
fuzz parser	0s
	32m 37s

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