NuGet(deps): Bump Discord.Net in /Izzy-MoonbotTests

Bumps [Discord.Net](https://github.com/discord-net/Discord.Net) from 3.15.0 to 3.15.2.
- [Release notes](https://github.com/discord-net/Discord.Net/releases)
- [Changelog](https://github.com/discord-net/Discord.Net/blob/dev/CHANGELOG.md)
- [Commits](discord-net/Discord.Net@3.15.0...3.15.2)

---
updated-dependencies:
- dependency-name: Discord.Net
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Izzy-Moonbot/Izzy-Moonbot.csproj

@@ -27,7 +27,7 @@
     </ItemGroup>
 
     <ItemGroup>
-        <PackageReference Include="Discord.Net" Version="3.15.0" />
+        <PackageReference Include="Discord.Net" Version="3.15.3" />
         <PackageReference Include="Flurl.Http" Version="3.2.4" />
         <PackageReference Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.21.0" />
         <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.0.0" />