ci: update Docker to 20.10 in our pipelines on CI/CD

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

.gitlab/ci/build.gitlab-ci.yml

@@ -2,9 +2,9 @@ build:
   extends:
     - .rules:except-docs
   stage: build
-  image: docker:19.03.5
+  image: docker:20.10.5
   services:
-    - docker:19.03.5-dind
+    - docker:20.10.5-dind
   before_script:
     - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" "$CI_REGISTRY"
   script:

.gitlab/ci/release.gitlab-ci.yml

@@ -10,9 +10,9 @@
 
 release-tag:
   stage: release
-  image: docker:19.03.5
+  image: docker:20.10.5
   services:
-    - docker:19.03.5-dind
+    - docker:20.10.5-dind
   script:
     - 'echo ${CI_JOB_TOKEN} | docker login --password-stdin -u $CI_REGISTRY_USER $CI_REGISTRY'
     - export ci_image="${CI_REGISTRY_IMAGE}"

.gitlab/ci/test.gitlab-ci.yml

@@ -422,9 +422,9 @@ test-chart-major-version-upgrade:
 test-upgrade-from-helm2-fails:
   extends:
     - .rules:except-docs
-  image: docker:19.03.12
+  image: docker:20.10.5
   services:
-    - docker:19.03.12-dind
+    - docker:20.10.5-dind
     - name: registry.gitlab.com/gitlab-org/cluster-integration/test-utils/k3s-gitlab-ci/releases/v1.16.7-k3s1
       alias: k3s
   interruptible: true