chore(deps): update docker.io/golang docker tag to v1.21.6 (#3189)

[![Mend
Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| docker.io/golang | patch | `1.21.5` -> `1.21.6` |

---

### Configuration

📅 **Schedule**: Branch creation - "every weekend" (UTC), Automerge -
"before 4am" (UTC).

🚦 **Automerge**: Enabled.

♻ **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.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

This PR has been generated by [Mend
Renovate](https://www.mend.io/free-developer-tools/renovate/). View
repository job log
[here](https://developer.mend.io/github/woodpecker-ci/woodpecker).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzNy4xMjcuMCIsInVwZGF0ZWRJblZlciI6IjM3LjEyNy4wIiwidGFyZ2V0QnJhbmNoIjoibWFpbiJ9-->

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.woodpecker/binaries.yaml

@@ -7,7 +7,7 @@ when:
   event: tag
 
 variables:
-  - &golang_image 'docker.io/golang:1.21.5'
+  - &golang_image 'docker.io/golang:1.21.6'
   - &node_image 'docker.io/node:21-alpine'
   - &xgo_image 'docker.io/techknowlogick/xgo:go-1.21.5'
   - &xgo_version 'go-1.21.2'

.woodpecker/docker.yaml

@@ -11,7 +11,7 @@ depends_on:
   - web
 
 variables:
-  - &golang_image 'docker.io/golang:1.21.5'
+  - &golang_image 'docker.io/golang:1.21.6'
   - &node_image 'docker.io/node:21-alpine'
   - &xgo_image 'docker.io/techknowlogick/xgo:go-1.21.5'
   - &xgo_version 'go-1.21.2'