update markdig version (#380)

Author: lyndaidaii

src/NuGet.Services.Messaging.Email/NuGet.Services.Messaging.Email.csproj

@@ -7,7 +7,7 @@
 
   <ItemGroup>
     <PackageReference Include="Markdig.Signed">
-      <Version>0.22.0</Version>
+      <Version>0.26.0</Version>
     </PackageReference>
     <PackageReference Include="NuGet.StrongName.AnglicanGeek.MarkdownMailer">
       <Version>1.2.0</Version>