Suppress VSTHRD003

See dotnet/roslyn#34331

eng/config/rulesets/Shipping.ruleset

@@ -163,6 +163,7 @@ collection.
   </Rules>
   <Rules AnalyzerId="Microsoft.VisualStudio.Threading.Analyzers" RuleNamespace="Microsoft.VisualStudio.Threading.Analyzers">
     <Rule Id="VSTHRD002" Action="None" /> <!-- Avoid problematic synchronous waits -->
+    <Rule Id="VSTHRD003" Action="None" /> <!-- Avoid awaiting foreign Tasks https://github.com/dotnet/roslyn/issues/34331 -->
     <Rule Id="VSTHRD103" Action="None" /> <!-- Call async methods when in an async method -->
     <Rule Id="VSTHRD010" Action="None" /> <!-- Invoke single-threaded types on Main thread https://github.com/dotnet/roslyn/issues/29275 -->
     <Rule Id="VSTHRD110" Action="None" /> <!-- Observe result of async calls -->