remove qt6gtk2 from AppImage (#620) #365

Job	Run time
appimage	35m 27s
cross-compile (arm-linux-musleabi)	15m 32s
cross-compile (arm-linux-musleabihf)	20m 47s
cross-compile (aarch64-linux-musl)	16m 31s
cross-compile (mips-linux-musl)	16m 7s
cross-compile (mipsel-linux-musl)	15m 59s
cross-compile (mips64-linux-musl)	16m 20s
cross-compile (mips64el-linux-musl)	15m 52s
cross-compile (x86_64-linux-musl)	21m 21s
cross-compile (i686-linux-musl)	20m 51s
	3h 14m 47s

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