Fix CI - curl unable to fetch server list

This is not a proper fix: Debian unstable's curl is either broken or is incompatible with MV build produced by gcc10 or we haven't fixed an incompatibility in ManaVerse.. but I saw no deprecation warnings anywhere.

If it's a true issue we'll stumble upon it when updating CIs in general, see #71.

Since gcc-snapshot is disabled, it should also save some CI time.

@ewewukek any comments? Otherwise I'm merging it ASAP.