Update the qemu-ga
Gentoo has a more recent version marked stable
Do not set SYNC variable to fix syncing via git

Setting the SYNC variable while the portage tree is a git repository
leads to the following error when doing `emerge --sync`:

```
>>> Synchronization of repository 'gentoo' located in '/usr/portage'...
!!! /usr/portage appears to be under revision control (contains .git).
!!! Aborting rsync sync.
```
Merge branch 'develop'