From https://www.dokuwiki.org/requirements

PHP needs to be at least version 7.2 since the “Igor” release, support for previous PHP versions has been dropped on this release. PHP versions up to and including 7.4 are now EOL, therefore using the latest version of the 7.4.x branch or 8.x is highly recommended. Dokuwiki is compatible with PHP 8.0 and 8.1.

<<<
Executing "step_script" stage of the job script 00:00
$ echo "$DOCKER_REGISTRY_PASS"|docker login $DOCKER_REGISTRY --username $DOCKER_REGISTRY_USER --password-stdin
Error: Cannot perform an interactive login from a non TTY device
>>>

We use shell executor.
This reverts commit 1a52e0df.

Image is busybox and do not contains bash or docker.

- Do not try to build missing tarballs
- Tag latest either stable or rc

From https://www.dokuwiki.org/install:upgrade

https://github.com/docker-library/php/issues/931

When cache is enabled, image is not rebuild when executing on the same runner.