glib2.0 (2.77.0 ) breaks Netplan build

Netplan FTBFS as of the latest release of glib2.0 (2.77.0-0ubuntu1) in mantic-proposed.

See: https://launchpad.net/ubuntu/+source/netplan.io/0.106.1-3

When I downgrade glib in my sbuild environment, everything works as expected:

$ apt install libglib2.0-0=2.76.3-1ubuntu1 libglib2.0-bin=2.76.3-1ubuntu1 libglib2.0-dev=2.76.3-1ubuntu1 libglib2.0-dev-bin=2.76.3-1ubuntu1 libglib2.0-data=2.76.3-1ubuntu1

The build also works fine in Debian unstable, which is using glib2.0 2.74.6-2.

Netplan is using plenty of GLib's keyfile functions (https://docs.gtk.org/glib/struct.KeyFile.html), which seem to producing a different output with this newer release (some strange line breaks injected in the middle of a keyfile).

Example keyfile from the test_wifis.test_wifi_wowlan test, that should be generated by Netplan and the way it fails:

Expected output:
```
[connection]
id=netplan-wl0-homenet
type=wifi
interface-name=wl0

[wifi]
wake-on-wlan=330
ssid=homenet
mode=infrastructure

[ipv4]
method=link-local

[ipv6]
method=ignore
```

Failure:
```
E AssertionError: '[con[88 chars]330\n\nssid=homenet\nmode=infrastructure\n[ipv[44 chars]re\n' != '[con[88 chars]330\nssid=homenet\nmode=infrastructure\n\n[ipv[44 chars]re\n'
E [connection]
E id=netplan-wl0-homenet
E type=wifi
E interface-name=wl0
E
E [wifi]
E wake-on-wlan=330
E -
E ssid=homenet
E mode=infrastructure
E +
E [ipv4]
E method=link-local
E
E [ipv6]
E method=ignore
```