Bump Microsoft.Net.Compilers.Toolset in /tools/DevicesApiTester (#1922)

Bumps [Microsoft.Net.Compilers.Toolset](https://github.com/dotnet/roslyn) from 4.2.0 to 4.3.0.
- [Release notes](https://github.com/dotnet/roslyn/releases)
- [Changelog](https://github.com/dotnet/roslyn/blob/main/docs/Breaking%20API%20Changes.md)
- [Commits](dotnet/roslyn@v4.2.0...Visual-Studio-2019-Version-16.0-Preview-4.3)

---
updated-dependencies:
- dependency-name: Microsoft.Net.Compilers.Toolset
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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eng/Compilers.props

@@ -4,7 +4,7 @@
     <UseSharedCompilation>true</UseSharedCompilation>
     <!-- Use the inbox compilers that come with the SDK -->
     <UseSdkCompilers>true</UseSdkCompilers>
-    <CompilerVersion>4.2.0</CompilerVersion>
+    <CompilerVersion>4.3.0</CompilerVersion>
   </PropertyGroup>
 
   <PropertyGroup>