Build

mintbackup.py: Fix gtk3 deprecation warnings. #8

Job	Run time
build / build (mint22, linuxmintd/mint22-amd64, Mint 22, true) / Mint 22	1m 43s
build / build (lmde6, linuxmintd/lmde6-amd64, LMDE 6, false) / LMDE 6	1m 46s
	3m 29s

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