cpubits: have `enable_64_bits` capture group name match attribute (#1… #340

Job	Run time
test-careful	1m 21s
build (1.85.0, thumbv7em-none-eabi)	18s
test (stable)	1m 36s
test (1.85.0)	1m 36s
build (1.85.0, wasm32-unknown-unknown)	19s
test-miri (s390x-unknown-linux-gnu)	1m 8s
build (stable, thumbv7em-none-eabi)	19s
build (stable, wasm32-unknown-unknown)	19s
test-miri (x86_64-unknown-linux-gnu)	54s
	7m 50s

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