Move .NET Docker projects to the .NET 9 TFM

[lbussell]

.NET Docker

• [x] update-dependencies
• [x] update-dependencies Dockerfile
• [x] Microsoft.DotNet.Docker.Tests

Docker tools

• [x] file-pusher
• [x] file-pusher Dockerfile
• [x] yaml-updater
• [x] yaml-updater Dockerfile
• [x] ImageBuilder
• [x] ImageBuilder Dockerfile
• [x] ImageBuilder Tests

[lbussell]

[Triage] This should wait until .NET 9 RC1 is GA.

[lbussell]

Moving to Rollout column since this should get merged from nightly to main with servicing release.