Jobs should be better isolated to avoid interference with other `image` or...

Jobs should be better isolated to avoid interference with other `image` or `before_script` statements.

changelogs/unreleased/patch-55.yml

+---
+title: Better isolated `Docker.gitlab-ci.yml` to avoid interference with other job configurations.
+merge_request: 28213
+author: lrkwz
+type: changed

lib/gitlab/ci/templates/Docker.gitlab-ci.yml

-# Official docker image.
-image: docker:latest
-
-services:
-  - docker:dind
-
-before_script:
-  - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
-
 build-master:
+  # Official docker image.
+  image: docker:latest
   stage: build
+  services:
+    - docker:dind
+  before_script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
   script:
     - docker build --pull -t "$CI_REGISTRY_IMAGE" .
     - docker push "$CI_REGISTRY_IMAGE"
@@ -16,7 +13,13 @@ build-master:
     - master
 
 build:
+  # Official docker image.
+  image: docker:latest
   stage: build
+  services:
+    - docker:dind
+  before_script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
   script:
     - docker build --pull -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" .
     - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"