.vsconfig update for .NET 4.8 (dotnet#51464)

.vsconfig was missing the missing
the .NET 4.8 Targetting pack option.

Fix dotnet#51455

Author: GilesDMiddleton

.vsconfig

@@ -30,6 +30,7 @@
     "Microsoft.Net.ComponentGroup.4.6.2.DeveloperTools",
     "Microsoft.Net.Component.4.7.TargetingPack",
     "Microsoft.Net.ComponentGroup.4.7.DeveloperTools",
+    "Microsoft.Net.Component.4.8.TargetingPack",
     "Microsoft.VisualStudio.Component.VC.CoreIde",
     "Microsoft.VisualStudio.Component.VC.Tools.x86.x64",
     "Microsoft.VisualStudio.Component.Windows10SDK.18362",
@@ -49,4 +50,4 @@
     "Microsoft.Net.Component.4.6.2.SDK",
     "Microsoft.Net.Component.4.7.SDK"
   ]
-}
+}