test: Re-Increase VM memory in TestMultiMachine
test: Re-Increase VM memory in TestMultiMachine

Commit 34f326ac34 reduced it to 512 MiB, but with that the test
sometimes runs into OOM on RHEL 8/9. Increase to 660 MiB, which still
stays inside the "2 GiB per test" limit.

martinpitt/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit