Update some packages and Unity reference files

Common.props

@@ -14,11 +14,11 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.2" />
-    <PackageReference Include="Nullable" Version="1.3.0">
+    <PackageReference Include="Nullable" Version="1.3.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="IsExternalInit" Version="1.0.2">
+    <PackageReference Include="IsExternalInit" Version="1.0.3">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
     </PackageReference>