Make SponsorLink diagnostics match the NG prefix

Makes it consistent with the diagnostics we emit, as well as build warnings.

Author: kzu

src/CodeAnalysis/SponsorLinker.cs

@@ -11,7 +11,8 @@ class SponsorLinker : SponsorLink
 {
     public SponsorLinker() : base(SponsorLinkSettings.Create(
         "devlooped", "NuGetizer",
-        version: new Version(ThisAssembly.Info.Version).ToString(2)
+        version: new Version(ThisAssembly.Info.Version).ToString(2),
+        diagnosticsIdPrefix: "NG"
 #if DEBUG
         , quietDays: 0
 #endif