docker: bump i386/golang in /unstable/build/alpine-x86

Bumps i386/golang from 1.21.4-alpine3.18 to 1.21.5-alpine3.18.

---
updated-dependencies:
- dependency-name: i386/golang
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

unstable/build/alpine-x86/Dockerfile

@@ -7,7 +7,7 @@
 
 # https://hub.docker.com/_/golang
 
-FROM i386/golang:1.21.4-alpine3.18
+FROM i386/golang:1.21.5-alpine3.18
 
 # https://docs.github.com/en/packages/learn-github-packages/connecting-a-repository-to-a-package
 LABEL org.opencontainers.image.source="https://github.com/atc0005/go-ci"