The system closure has grown slightly above 1GiB so adjust accordingly.
* gnu/tests/install.scm (%simple-installation-script): Increase vdb2 size of
1.2G,
(%extlinux-gpt-installation-script); ditto
(%simple-installation-script-for-/dev/vda): ditto,
(%separate-store-installation-script): ditto for vdb3,
(%encrypted-root-installation-script): ditto.