Don't ship blazor packages from release/3.1 (#17342)

Author: wtgodbe

src/Components/Blazor/Directory.Build.props

@@ -4,6 +4,8 @@
   <PropertyGroup>
     <!-- Override prerelease label and use preview 4, even in the final build -->
     <PreReleaseVersionLabel>$(BlazorClientPreReleaseVersionLabel)</PreReleaseVersionLabel>
+    <!-- These packages ship from the blazor-wasm branch -->
+    <IsShipping>false</IsShipping>
     <DotNetFinalVersionKind></DotNetFinalVersionKind>
   </PropertyGroup>
 </Project>