avro

AVRO-4079: Remove not needed libssl trickery, what was required by C# NET 3.1 and 5.0 (#3215)

* Remove netcoreapp3.1 and 5.0 support

* Revert to ubuntu-latest

* Remove libssl trickery

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Co-authored-by: Zoltan Csizmadia <Zoltan.Csizmadia@vericast.com>