Fix packaging compat target generation (#73555)

Fixes #73463. Tested locally just now.

Author: ViktorHofer

eng/packaging.targets

@@ -200,7 +200,7 @@
 <![CDATA[<Project InitialTargets="$(_NETStandardCompatErrorFileTarget)">
   <Target Name="$(_NETStandardCompatErrorFileTarget)"
           Condition="'%24(SuppressTfmSupportBuildWarnings)' == ''">
-    <Warning Text="$(PackageId) $(PackageVersion) doesn't support %24(TargetFramework) and has not been tested with it. Consider upgrading your TargetFramework to %(NETStandardCompatError.Supported) or later. You may also set &lt;SuppressTfmSupportBuildWarnings&gt;true&lt;/SuppressTfmSupportBuildWarnings&gt; in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk." />
+    <Warning Text="$(PackageId) $(PackageVersion) doesn't support %24(TargetFramework) and has not been tested with it. Consider upgrading your TargetFramework to %(NETStandardCompatError.Supported) or later. You may also set &lt%3BSuppressTfmSupportBuildWarnings&gt%3Btrue&lt%3B/SuppressTfmSupportBuildWarnings&gt%3B in the project file to ignore this warning and attempt to run in this unsupported configuration at your own risk." />
   </Target>
 </Project>]]>
       </_NETStandardCompatErrorFileContent>