Add C# 8 Build Step

[jamescourtney]

No description provided.

[codecov]

Codecov Report

Merging #362 (24621ce) into main (2515d92) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #362   +/-   ##
=======================================
  Coverage   96.61%   96.62%           
=======================================
  Files         114      114           
  Lines        8698     8701    +3     
  Branches      810      810           
=======================================
+ Hits         8404     8407    +3     
  Misses        203      203           
  Partials       91       91           

Impacted Files	Coverage Δ
...harp.Compiler/SchemaModel/RpcServiceSchemaModel.cs	98.98% <100.00%> (+<0.01%)	⬆️

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