Task returns true and logs error results in successful builds in unit tests

### Issue Description
In WarningsAsMessagesAndErrors_Tests.cs, you can create a test scenario that has a task return true and log an error, and the build result is a success instead of a failure.

### Steps to Reproduce
Add this test class:
```
// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;
namespace Microsoft.Build.UnitTests
{
public class CustomLogAndReturnTask : Task
{
public string WarningCode { get; set; }

public string ErrorCode { get; set; }

public bool ReturnHasLoggedErrors { get; set; }

[Required]
public bool Return { get; set; }

///
/// This task returns and logs what you want based on the running test.
///
public override bool Execute()
{
if(!string.IsNullOrEmpty(WarningCode))
{
Log.LogWarning(null, WarningCode, null, null, 0, 0, 0, 0, "Warning Logged!", null);
}

if(!string.IsNullOrEmpty(ErrorCode))
{
Log.LogError(null, ErrorCode, null, null, 0, 0, 0, 0, "Error Logged!", null);
}
return ReturnHasLoggedErrors ? !Log.HasLoggedErrors : Return;
}
}
}
```

Add this test case:
```
///
/// This is incredibly confusing and shouldn't work this way. This was also tested
/// in latest master (6819f7a) and passed. Keeping this test here for visibility.
/// This specific scenario does not repro when building a standard project with a bootstrapped MSBuild.
///
[Fact]
public void TaskReturnsTrueButLogsError_BuildShouldFinishAndFail()
{
using (TestEnvironment env = TestEnvironment.Create(_output))
{
TransientTestProjectWithFiles proj = env.CreateTestProjectWithFiles($@"






");

// What????
MockLogger logger = proj.BuildProjectExpectSuccess();

logger.WarningCount.ShouldBe(1);
logger.ErrorCount.ShouldBe(1);

// The build should CONTINUE when a task returns true.
logger.AssertLogContains("MSB1234");
}
}
```

### Expected Behavior
This test will pass, though it should fail.

### Actual Behavior
Here's the output log:
```
Build started.
Project "build.proj" (default targets):
Building with tools version "Current".
Target "Build" in project "C:\Users\bevillal\AppData\Local\Temp\jjik1gim.uf1\Temporary916c230401364e6faec586e2a834d69e\build.proj" (entry point):
Using "CustomLogAndReturnTask" task from assembly "Microsoft.Build.Engine.UnitTests".
Task "CustomLogAndReturnTask"
C:\Users\bevillal\AppData\Local\Temp\jjik1gim.uf1\Temporary916c230401364e6faec586e2a834d69e\build.proj(5,25): error MSB1235: Error Logged!
Done executing task "CustomLogAndReturnTask".
Task "CustomLogAndReturnTask"
C:\Users\bevillal\AppData\Local\Temp\jjik1gim.uf1\Temporary916c230401364e6faec586e2a834d69e\build.proj(6,25): warning MSB1234: Warning Logged!
Done executing task "CustomLogAndReturnTask".
Done building target "Build" in project "build.proj".
Done building project "build.proj".
Build succeeded.

```

### Analysis
This does not happen in live scenarios. Simply build this project that has a task called CustomLogAndReturnTask (same as above).
```

```
You should see that the build failed.

### Versions & Configurations
Happens in latest master as of 6819f7a.