EventAggregator.Tests: use hardcoded dep version

This commit fixes the issue caused by YoloDev.Expecto.TestSdk
upgrade to netcoreapp3.1.

Author: aarani

tests/EventAggregator.Tests/EventAggregator.Tests.fsproj

@@ -12,10 +12,10 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Expecto" Version="8.*" />
-    <PackageReference Include="FSharp.Core" Version="4.*" />
-    <PackageReference Include="YoloDev.Expecto.TestSdk" Version="0.*" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.*" />
+    <PackageReference Include="Expecto" Version="8.13.2" />
+    <PackageReference Include="FSharp.Core" Version="4.7.2" />
+    <PackageReference Include="YoloDev.Expecto.TestSdk" Version="0.12.20" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.11.0" />
   </ItemGroup>
 
   <ItemGroup>