Merged PR 22672: Ignore CFS warning since the pipeline works around it

The build pipeline replaces the nuget.config with one that is compliant with the CFS requirement that Azure Pipelines pull from Azure nuget feeds instead of directly from nuget.org.

This change will be reverted once a public Azure nuget feed exists for Win2D, but this will temporarily unblock builds.

.sscignore

@@ -0,0 +1 @@
+{ "cfs": ["CFS0013"] }

tools/checkcode/RunCodeChecks.proj

@@ -31,7 +31,7 @@
     <!-- File extensions and directories to check vs. ignore -->
     <CppExt>c;cpp;h;inl;cs;idl;rc;hlsl</CppExt>
     <XmlExt>xml;xaml;aml</XmlExt>
-    <SkipExt>;gitattributes;gitignore;orig;jpg;png;dds;txt;md;pfx;cmd;bat;proj;nuspec;props;targets;def;sln;csproj;vcxproj;vcxitems;filters;projitems;shproj;shfbproj;content;config;appxmanifest;suo;ipch;sdf;log;opensdf;user;exe;bmp;ico;tif;vsdx;svg;json;bin;opendb;db;binlog;vsconfig_buildtools;ps1</SkipExt>
+    <SkipExt>;gitattributes;gitignore;orig;jpg;png;dds;txt;md;pfx;cmd;bat;proj;nuspec;props;targets;def;sln;csproj;vcxproj;vcxitems;filters;projitems;shproj;shfbproj;content;config;appxmanifest;suo;ipch;sdf;log;opensdf;user;exe;bmp;ico;tif;vsdx;svg;json;bin;opendb;db;binlog;vsconfig_buildtools;ps1;sscignore</SkipExt>
     <SkipDir>.git;obj;bin;TestResults;build;.nuget;packages;.vs;.vscode</SkipDir>
 
     <!-- Commandline arguments for the CheckCode.exe tool -->