chore(deps): update docker.io/alpine docker tag to v3.20

.woodpecker/docs.yaml

@@ -1,7 +1,7 @@
 variables:
   - &golang_image 'docker.io/golang:1.23'
   - &node_image 'docker.io/node:22-alpine'
-  - &alpine_image 'docker.io/alpine:3.19'
+  - &alpine_image 'docker.io/alpine:3.20'
   - path: &when_path
       - 'docs/**'
       - '.woodpecker/docs.yaml'