Update mcr.microsoft.com/dotnet/sdk Docker tag to v9

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
mcr.microsoft.com/dotnet/sdk	stage	major	7.0-alpine -> 9.0-alpine

---

Configuration

📅 Schedule: Branch creation - "before 07:00 on Thursday" in timezone Europe/Oslo, Automerge - At any time (no schedule defined).

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

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

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

---

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

---

This PR was generated by Mend Renovate. View the repository job log.

[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.