build: Update dotnet-core.yml to use dotnet version 8.0.x

Author: leonibr

.github/workflows/dotnet-core.yml

@@ -14,8 +14,6 @@ jobs:
         uses: actions/setup-dotnet@v1
         with:
           dotnet-version: |
-            6.0.x
-            7.0.x
             8.0.x
 
       - name: Install dependencies