Remove .NET 5 TFM

[devlead]

.NET 5 is now out of support and should be removed next major release of Cake

[devlead]

@Marusyk need a reply in this issue from you before GitHub lets me assign you.
You can do #3972 and this in one PR but two commits after #3990 is merged and #3950 closed.

[Marusyk]

ok

[devlead]

ok

Excellent issue now assigned to you, and .NET 7 support already merged.

[cake-build-bot]

🎉 This issue has been resolved in version v3.0.0 🎉

The release is available on:

• GitHub Release
• .NET Tool

Your GitReleaseManager bot 📦🚀