appveyor - Set ContinuousIntegrationBuild when running on appveyor

https://learn.microsoft.com/en-us/dotnet/core/project-sdk/msbuild-props#continuousintegrationbuild

Author: amaitland

lib/PuppeteerSharp/CefSharp.Dom.csproj

@@ -38,6 +38,10 @@
     <PackageReference Include="CefSharp.Common.NETCore" Version="104.4.180" />
   </ItemGroup>
 
+  <PropertyGroup Condition="'$(APPVEYOR)' == 'True'">
+    <ContinuousIntegrationBuild>true</ContinuousIntegrationBuild>
+  </PropertyGroup>
+
   <ItemGroup>
     <None Include="..\..\README.md" Link="README.md" Pack="true" PackagePath="\" />
   </ItemGroup>