Update Microsoft.VisualStudio.SDK requirement from 17.2.* to 17.3.*

Updates the requirements on Microsoft.VisualStudio.SDK to permit the latest version.

---
updated-dependencies:
- dependency-name: Microsoft.VisualStudio.SDK
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

src/Xunit.Vsix.Tests/Xunit.Vsix.Tests.csproj

@@ -40,7 +40,7 @@
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" />
     <PackageReference Include="IsExternalInit" Version="1.0.3" PrivateAssets="all" />
     <PackageReference Include="NuGet.Versioning" Version="6.3.0" />
-    <PackageReference Include="Microsoft.VisualStudio.SDK" Version="17.2.*" />
+    <PackageReference Include="Microsoft.VisualStudio.SDK" Version="17.3.*" />
     <PackageReference Include="Octokit" Version="2.0.1" />
     <PackageReference Include="ThisAssembly.Project" Version="1.0.9" />
   </ItemGroup>