Comment 4 for bug 1805203

Faced same issue and solved by downgrading.

To avoid upgrade of package and adding bionic-security to sources list One can do:
1. Manually download package from https://packages.ubuntu.com/bionic/libcurl3-gnutls
2. Install libcurl3-gnutls with dpkg -i libcurl3-gnutls*.deb
3. Lock package version with apt-mark hold libcurl3-gnutls
4. Once update will be pushed just unlock package with apt-mark unhold libcurl3-gnutls