Version up

.gitlab-ci.yml

-image: docker:19.03.1
+image: docker:19.03.12
 
 variables:
   DOCKER_TLS_CERTDIR: "/certs"
-  IMAGE_TAG: $CI_REGISTRY_IMAGE:latest
+  IMAGE_VER: 3.26.5
 
 services:
-  - docker:19.03.1-dind
+  - docker:19.03.12-dind
 
 before_script:
   - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
@@ -13,5 +13,7 @@ before_script:
 build:
   stage: build
   script:
-    - docker build -t $IMAGE_TAG .
-    - docker push $IMAGE_TAG
+    - docker pull $CI_REGISTRY_IMAGE:latest || true
+    - docker build --cache-from $CI_REGISTRY_IMAGE:latest --tag $CI_REGISTRY_IMAGE:$IMAGE_VER --tag $CI_REGISTRY_IMAGE:latest .
+    - docker push $CI_REGISTRY_IMAGE:$IMAGE_VER
+    - docker push $CI_REGISTRY_IMAGE:latest

Dockerfile

 FROM php:7.2-apache
 LABEL maintainer="markus@martialblog.de"
-ARG version='3.21.0+191203'
-ARG sha256_checksum='3511e44fbc39372501f933d6188f161d53464120337e69d15c735f1b2f78e287'
+ARG version='3.26.5+210519'
+ARG sha256_checksum='fbe6c59b6b23f34f1d9dbc8ca64dfb4ce8573cc0925e9aad2db00c6b0d4b62fd'
 
 # Install OS dependencies
 RUN set -ex; \