Recognize '.jfif' extension as JPEG file #1648

Job	Run time
build_benchmarks	46s
cargo-deny	19s
Fuzz targets (afl)	2m 12s
Fuzz targets (cargo-fuzz)	52s
cargo-semver-checks	28s
clippy	1m 58s
public_private_dependencies	24s
rustfmt	4s
test_avif_decoding	1m 36s
test_other_archs (powerpc-unknown-linux-gnu)	2m 49s
test_features	25s
test_other_archs (i686-unknown-linux-gnu)	1m 35s
test_toolchains (1.70.0)	32s
test_features (default)	1m 48s
test_toolchains (nightly)	1m 43s
test_features (rayon)	42s
test_toolchains (beta)	1m 38s
test_features (avif)	59s
test_features (bmp)	40s
test_features (dds)	32s
test_features (exr)	46s
test_features (ff)	31s
test_features (gif)	39s
test_features (hdr)	32s
test_features (ico)	49s
test_features (jpeg)	33s
test_features (png)	36s
test_features (pnm)	33s
test_features (qoi)	34s
test_features (tga)	36s
test_features (tiff)	41s
test_features (webp)	34s
	29m 26s

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