Build errors in VSCode appear twice

## Environment data
```
.NET Core SDK (reflecting any global.json):
Version: 3.1.201
Commit: b1768b4ae7

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.1.201\

Host (useful for support):
Version: 3.1.3
Commit: 4a9f85e9f8

.NET Core SDKs installed:
3.1.201 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
```

## Steps to reproduce
Create a new dotnet core project using `dotnet new console`
Select yes to generate tasks.json and launch.json defaults
Remove the semicolon in the auto-generated Hello World code
Run the build task

## Expected behavior
Only one `CS1002` error saying "; expected"

## Actual behavior
Two `CS1002` errors pointing to the same line, one with an included full path, another without one

## Screenshots