Build

Add Flatpak modify-repo action (#71) #103

Job	Run time
build / build (lmde7, linuxmintd/lmde7-amd64, LMDE 7, false) / LMDE 7	2m 7s
build / build (mint22, linuxmintd/mint22.3-amd64, Mint 22, true) / Mint 22	1m 44s
generate-test-packages	-10s
	3m 41s

Provide feedback