Bump golang from 1.20.7-alpine to 1.22.2-alpine in /docker/staging

Bumps golang from 1.20.7-alpine to 1.22.2-alpine.

---
updated-dependencies:
- dependency-name: golang
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

docker/staging/Dockerfile

@@ -1,7 +1,7 @@
 # syntax = docker/dockerfile:1.3.0
 
 # build backend
-FROM golang:1.20.7-alpine as server-build
+FROM golang:1.22.2-alpine as server-build
 RUN --mount=type=cache,target=/var/cache/apk \
   apk add --update git