build: update Go to 1.27 (#26451)

Update `GO_VERSION` from 1.26 to 1.27 in the root and releaser
Dockerfiles. Keep the floating minor-version image tags used in
6a093939d4 and da3893027f; both 1.27 tags resolve to Go 1.27.3 on
October 26, 2026. Unlike those broader updates, this PR leaves module
files and the Go version used in documentation examples unchanged.

Docker Agent v1.151.0 and later require Go 1.27. The official Go image
sets `GOTOOLCHAIN=local`, so the Go 1.26 build cannot vendor those
releases. Daily `sync-docker-agent-docs` runs have failed since at least
October 24, 2026; the [October 26
run](https://github.com/docker/docs/actions/runs/40261071727) reports
this version mismatch while vendoring v1.152.0.

#26368 will be stacked on this PR to sync Docker Agent v1.152.0 and fix
the Community links. Merge this toolchain upgrade first.

Validation: `dockerfile-lint`, `releaser-build`, `releaser-test` (9
tests), and `validate-api-reference` passed with `docker buildx bake`.
Local `validate-vendor` and `test` hit the existing Community vendor
mismatch and nine missing references from the separately applied #26368
changes. CI on this isolated two-line PR is the authoritative check for
those targets.

Dockerfile

@@ -2,7 +2,7 @@
 # check=skip=InvalidBaseImagePlatform
 
 ARG ALPINE_VERSION=3.23
-ARG GO_VERSION=1.26
+ARG GO_VERSION=1.27
 ARG HTMLTEST_VERSION=0.17.0
 ARG VALE_VERSION=3.17.0
 ARG HUGO_VERSION=0.163.0

hack/releaser/Dockerfile

@@ -1,6 +1,6 @@
 # syntax=docker/dockerfile:1
 
-ARG GO_VERSION=1.26
+ARG GO_VERSION=1.27
 
 FROM scratch AS sitedir