Update golang Docker tag to v1.21.6

Created by: renovate[bot]

This PR contains the following updates:

Package	Type	Update	Change
golang	stage	patch	1.21.5-bullseye -> 1.21.6-bullseye
golang		patch	1.21.5 -> 1.21.6

---

Release Notes

golang/go (golang)

v1.21.6

Compare Source

---

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 becomes conflicted, or you tick the rebase/retry checkbox.

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

---

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

---

This PR has been generated by Mend Renovate. View repository job log here.