regex-lite: fix compilation of doctests on 32-bit architectures #1937

Job	Run time
miri-regex-automata	10m 35s
msrv	4m 16s
test (stable, ubuntu-latest, stable)	7m 15s
rustfmt	24s
test (stable-32, ubuntu-latest, stable, i686-unknown-linux-gnu)	6m 20s
testfull-regex	8m 55s
test (stable-powerpc64, ubuntu-latest, stable, powerpc64-unknown-linux-gnu)	14m 22s
testfull-regex-automata	15m 7s
test (stable-s390x, ubuntu-latest, stable, s390x-unknown-linux-gnu)	13m 49s
testfull-regex-capi	58s
testfull-regex-syntax	4m 0s
test (beta, ubuntu-latest, beta)	6m 54s
test (nightly, ubuntu-latest, nightly)	7m 18s
test (macos, macos-latest, stable)	7m 12s
test (win-msvc, windows-latest, stable)	9m 51s
test (win-gnu, windows-latest, stable-x86_64-gnu)	6m 8s
	2h 3m 24s

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