Temporarily disable PCX format #1701

Job	Run time
cargo-deny	19s
Fuzz targets (afl)	2m 44s
Fuzz targets (cargo-fuzz)	49s
build_benchmarks	48s
cargo-semver-checks	39s
clippy	1m 58s
public_private_dependencies	26s
rustfmt	5s
test_avif_decoding	1m 24s
test_features	29s
test_other_archs (powerpc-unknown-linux-gnu)	3m 7s
test_features (default)	1m 55s
test_toolchains (1.70.0)	34s
test_other_archs (i686-unknown-linux-gnu)	1m 55s
test_features (rayon)	27s
test_toolchains (nightly)	1m 40s
test_features (avif)	1m 11s
test_toolchains (beta)	1m 43s
test_features (bmp)	37s
test_features (dds)	30s
test_features (exr)	43s
test_features (ff)	30s
test_features (gif)	33s
test_features (hdr)	31s
test_features (ico)	39s
test_features (jpeg)	31s
test_features (pcx)	21s
test_features (png)	39s
test_features (pnm)	29s
test_features (qoi)	23s
test_features (tga)	25s
test_features (tiff)	32s
test_features (webp)	43s
	30m 19s

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