Fix webp benches #953

Job	Run time
cargo-deny	35s
build_benchmarks	1m 31s
Fuzz targets (afl)	2m 45s
Fuzz targets (cargo-fuzz)	8m 30s
clippy	3m 29s
public_private_dependencies	27s
rustfmt	20s
test_avif	2m 17s
test_avif_decoding	2m 12s
test_big_endian	1m 26s
test_big_endian (default)	5m 14s
test_big_endian (webp)	1m 49s
test_big_endian (webp-encoder)	3m 4s
test_features	41s
test_features (default)	1m 56s
test_features (gif)	44s
test_features (jpeg)	53s
test_features (png)	42s
test_features (tiff)	48s
test_features (ico)	1m 2s
test_features (pnm)	38s
test_features (tga)	34s
test_features (webp)	45s
test_features (bmp)	42s
test_features (hdr)	40s
test_features (dxt)	38s
test_features (dds)	41s
test_features (farbfeld)	44s
test_features (openexr)	1m 16s
test_features (jpeg_rayon)	58s
test_features (webp-encoder)	1m 17s
test_toolchains (1.61.0)	46s
test_toolchains (nightly)	3m 56s
test_toolchains (beta)	2m 13s
verify_msrv	2m 32s
	58m 45s

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