ci: fix Go job — golang:1.23-trixie does not exist on Docker Hub, use golang:1.23-alpine3.21 (git 2.47+, sha256-capable)

.forgejo/workflows/validate.yml

@@ -118,13 +118,13 @@ jobs:
     name: Go (vet + test)
     runs-on: ubuntu-latest
     container:
-      image: golang:1.23-trixie
+      # Alpine image: git 2.45+, speaks sha256 wire protocol; small footprint.
+      image: golang:1.23-alpine3.21
     steps:
-      - name: Install git + curl in container
+      - name: Install git + bash in container
         run: |
-          set -euo pipefail
-          apt-get update
-          apt-get install -y --no-install-recommends git curl ca-certificates
+          set -eu
+          apk add --no-cache git bash ca-certificates
           git --version
           go version