otd: Build using .NET 8, but require .NET 6 at runtime

[korewaChino]

This change is required because newer versions of Fedora do not have .NET 6.0 in the repositories, but we can still build .NET 6.0 applications using the .NET 8.0 SDK.

A long-term solution here is to get upstream to port their code to a newer .NET version, or we package .NET 6.0 for newer versions of Fedora. Upstream master branch targets .NET 8, but it has not been released yet. We need a nightly package for this

.NET 6.0 will be EOL in November 12, 2024.

[raboneko]

💔 Some backports could not be created

Status	Branch	Result
✅	f39
✅	f40
✅	f41
❌	el9	Backport failed because of merge conflicts

Manual backport

To create the backport manually run:

backport --pr 1967

Questions ?

Please refer to the Backport tool documentation and see the Github Action logs for details