Update NuGet.PackageManagement to 6.3.1

Author: AArnott

src/nbgv/nbgv.csproj

@@ -10,7 +10,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="NuGet.PackageManagement" Version="5.11.0" />
+    <PackageReference Include="NuGet.PackageManagement" Version="6.3.1" />
     <PackageReference Include="System.CommandLine" Version="2.0.0-beta1.20574.7" />
     <PackageReference Include="Nerdbank.GitVersioning.LKG" Version="3.4.173-alpha" PrivateAssets="all" />
     <PackageReference Include="System.Diagnostics.Tools" Version="4.3.0" />