appstream: Only provide screenshots at 1x scale. #121

Job	Run time
build / build (lmde6, linuxmintd/lmde6-amd64, LMDE 6, false) / LMDE 6	13m 53s
build / build (mint22, linuxmintd/mint22-amd64, Mint 22, true) / Mint 22	16m 6s
	29m 59s

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