Tests(Console): fix bug in tests

Fix bug in tests where empty sets of different types would be
treated as different.

Error was:
```
Expected is <Microsoft.FSharp.Collections.FSharpSet`1[System.IComparable]>, actual is <Microsoft.FSharp.Collections.FSharpSet`1[System.String]>
```

tests/FSharpLint.Console.Tests/TestApp.fs

@@ -80,7 +80,7 @@ type TestConsoleApplication() =
         let (returnCode, errors) = main [| "lint"; "--lint-config"; config.FileName; input |]
 
         Assert.AreEqual(0, returnCode)
-        Assert.AreEqual(Set.empty, errors)
+        Assert.IsEmpty errors
 
     [<Test>]
     member __.``Lint source with error suppressed, no error is given.``() =
@@ -94,7 +94,7 @@ type TestConsoleApplication() =
         let (returnCode, errors) = main [| "lint"; input |]
 
         Assert.AreEqual(0, returnCode)
-        Assert.AreEqual(Set.empty, errors)
+        Assert.IsEmpty errors
 
     [<Test>]
     member __.``Regression test: typePrefixing rule with old config format should still work``() =