Update dotnet monorepo to v9 (major)

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
mcr.microsoft.com/dotnet/aspnet	final	major	8.0 -> 9.0
mcr.microsoft.com/dotnet/runtime-deps	final	major	8.0 -> 9.0
mcr.microsoft.com/dotnet/sdk	stage	major	8.0 -> 9.0
mcr.microsoft.com/dotnet/sdk	final	major	8.0 -> 9.0

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Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about these updates again.

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• If you want to rebase/retry this PR, check this box

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[renovate]

Renovate Ignore Notification

Because you closed this PR without merging, Renovate will ignore this update. You will not get PRs for any future 9.x releases. But if you manually upgrade to 9.x then Renovate will re-enable minor and patch updates automatically.

If you accidentally closed this PR, or if you changed your mind: rename this PR to get a fresh replacement PR.