Suppress advisory for HtmlSanitizer (#6970)

It does not apply to our usage and requires a major version bump of
System.Collections.Immutable

Author: bdukes

DNN Platform/Library/DotNetNuke.Library.csproj

@@ -23,6 +23,7 @@
     <PackageReference Include="AngleSharp" />
     <PackageReference Include="AngleSharp.Css" />
     <PackageReference Include="BouncyCastle.Cryptography" />
+    <NuGetAuditSuppress Include="https://github.com/advisories/GHSA-j92c-7v7g-gj3f" />
     <PackageReference Include="HtmlSanitizer" />
     <PackageReference Include="MailKit" />
     <PackageReference Include="Microsoft.AspNet.WebPages" />