tests/image: give the test VM only 1 GB of memory

The VM doesn't need 2 GBs to start Fedora and ssh server. This fix enables
us to run the tests in more constrained environment.

cmd/osbuild-image-tests/context-managers.go

@@ -90,7 +90,7 @@ func withBootedQemuImage(image string, ns netNS, f func() error) error {
 
 		qemuCmd := ns.NamespacedCommand(
 			"qemu-system-x86_64",
-			"-m", "2048",
+			"-m", "1024",
 			"-snapshot",
 			"-accel", "accel=kvm:hvf:tcg",
 			"-cdrom", cloudInitFile.Name(),