dep: flag IDisposableAnalyzers as private, bump version

src/Discord.Net.Core/Discord.Net.Core.csproj

@@ -12,7 +12,7 @@
     <PackageReference Include="System.Collections.Immutable" Version="1.3.1" />
     <PackageReference Include="System.Interactive.Async" Version="3.1.1" />
   </ItemGroup>
-  <ItemGroup Condition=" '$(Configuration)' != 'Release' ">
-    <PackageReference Include="IDisposableAnalyzers" Version="2.0.3.3" />
-  </ItemGroup>
+  <PackageReference Include="IDisposableAnalyzers" Version="2.1.2">
+    <PrivateAssets>all</PrivateAssets>
+  </PackageReference>
 </Project>