tests: fix firewall tests after 6e8e48e3 "Avoid UTC datetime"
tests: fix firewall tests after 6e8e48e3 "Avoid UTC datetime"

marmarek/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin