chore(deps): update golang docker tag to v1.27.2 (#198)

## Summary

`k8s/deploy.yaml` takes the image from build-tools: `image: ${IMAGE}` instead of the hard-coded `oci.unbound.se/dancefinder/dancefetcher:${COMMIT}`.

`deploy` substitutes `${IMAGE}` with `<registry>/<owner>/<name>:<tag>`, where the registry comes from the build-tools config and the tag is the value `${COMMIT}` gets today. The rendered reference is unchanged. Moving off `oci.unbound.se` later becomes one change in infra.

Validated on shiny/time-service#864: merged and deployed to AWS staging and Frostmoln staging with the same image. Prerequisites, all merged:
- unboundsoftware/infra#1808: registry in `BUILDTOOLS_FROSTMOLN_STAGING`
- shiny/acctest#952: acctest pins build-tools to the Gitea registry

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://gitea.unbound.se/dancefinder/dancefetcher/pulls/196

Dockerfile

@@ -1,4 +1,4 @@
-FROM amd64/golang:1.27.1@sha256:2c9f73fbc9fe381c63ba57bcbab4ea1c9135604011985a0891bc5fe5d1febfca as build
+FROM amd64/golang:1.27.2@sha256:9e036bef9c3cd035cae4aeff523b3997c3c8aa993b13d112a71ea90143e87e48 as build
 WORKDIR /build
 ENV CGO_ENABLED=0
 ADD . /build