Update dependencies & Support Rider 2023.2 and .NET 8

[TSRBerry]

This PR contains a lot of changes but they are pretty simple to break down:

• Dependencies:
  • All the GitHub Action dependencies have been updated
  • All the backend dependencies have been updated (including code changes to make the backend compatible with the new NUnit version)
  • All the plugin dependencies have been updated
• Plugin:
  • The plugin files have been updated according to the latest intellij-platform-plugin-template commit
  • /usr/bin/dotnet has been added as another default path for the dotnet CLI for Linux systems
  • An exclusion for the slf4-api package has been added to prevent another NoClassDefFoundError
  • pluginSinceBuild has been raised to 231 and platformVersion has been set to 231.9225.16, since runPluginVerifier found incompatibilities with older versions when I forked the repo initially.
  • pluginVersion has been updated to 231.5.0
• Backend:
  • Support for .NET 8 and CSharp12 has been added

I created a test release with all these changes here.

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Closes #263

[ykoellmann]

Would be amazing if support for 2024.1 version would be added

[TSRBerry]

I'll look into that when I'm home again.