Revert change of setup version for netcoreapp2.0 + set exact version of netcoreapp3.1

Author: alex-kulakov

.github/actions/setup-dotnets/action.yml

@@ -45,10 +45,10 @@ runs:
       if: ${{ contains(inputs.target_framework, '3.1') }}
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: '3.1.x'
+        dotnet-version: '3.1.402'
 
     - name: Setup .NET Core 2.0 (if needed)
       if: ${{ contains(inputs.target_framework, '2.0') }}
       uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: '3.1.402'
+        dotnet-version: '2.1.403'