cleanup: Be selective about image formats in appimage as well. #536

Job	Run time
build (alpine-s390x)	18s
buildfarm (server)	20s
build (bazel)	3m 12s
buildfarm (worker)	19s
build (compcert)	18s
build (doxygen)	30s
qtox-host-qt (6.2.4)	23s
build (flutter-web)	17s
qtox-host-qt (6.8.1)	29s
build (frama-c)	14s
build (freebsd)	16s
build (haskell)	17s
build (pkgsrc)	20s
qtox (alpine)	21s
qtox-android (armeabi-v7a, debug, 6.2.4)	22s
qtox (alpine-appimage)	54s
qtox-android (armeabi-v7a, debug, 6.8.1)	17s
qtox (alpine-static)	22s
qtox-android (armeabi-v7a, release, 6.2.4)	20s
qtox (debian)	26s
qtox-android (armeabi-v7a, release, 6.8.1)	13s
qtox (fedora)	26s
qtox-android (arm64-v8a, debug, 6.2.4)	25s
qtox (flatpak-builder)	29s
qtox-android (arm64-v8a, debug, 6.8.1)	21s
qtox (ubuntu-lts)	23s
qtox-android (arm64-v8a, release, 6.2.4)	29s
qtox (windows-builder.i686)	22s
qtox-android (arm64-v8a, release, 6.8.1)	21s
qtox (windows-builder.x86_64)	22s
	14m 6s

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