Ensure iOS project builds in VS Mac by adding SkipValidatePackageReferences entry to .csproj.

src/Mobile/eShopOnContainers/eShopOnContainers.iOS/eShopOnContainers.iOS.csproj

@@ -13,6 +13,7 @@
     <AssemblyName>eShopOnContainersiOS</AssemblyName>
     <NuGetPackageImportStamp>
     </NuGetPackageImportStamp>
+    <SkipValidatePackageReferences>true</SkipValidatePackageReferences>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|iPhoneSimulator' ">
     <DebugSymbols>true</DebugSymbols>