Kubernetes runner outputs ENV variable name rather than values
### Summary
When using a Kubernetes runner to execute any security analyzer, the runner logs which image it is using without interpolating the ENV variables.
For example, a Kubernetes DAST job logs:
```
Using Kubernetes executor with image $SECURE_ANALYZERS_PREFIX/dast:$DAST_VERSION ...
```
Whereas the docker runner logs:
```
Using Docker executor with image registry.gitlab.com/gitlab-org/security-products/dast:1 ...
```
### Steps to reproduce
* Create a new project (The project can be based on https://gitlab.com/craigmsmith/craigmsmith-autodevops)
* Link to a Kubernetes cluster
* Install the Kubernetes runner
* Disable shared runners for the project (to ensure all the jobs run using the Kubernetes runner)
* run a build
* Once the build has completed, look at the DAST job log.
### Example Project
https://gitlab.com/craigmsmith/craigmsmith-autodevops/-/jobs/559737224#L5
### What is the current *bug* behavior?
```
Using Kubernetes executor with image $SECURE_ANALYZERS_PREFIX/dast:$DAST_VERSION ...
```
is output to the log
### What is the expected *correct* behavior?
```
Using Kubernetes executor with image registry.gitlab.com/gitlab-org/security-products/dast:1 ...
```
should be output to the log
### Relevant logs and/or screenshots
(Paste any relevant logs - please use code blocks (```) to format console output,
logs, and code as it's tough to read otherwise.)
### Output of checks
This bug happens on GitLab.com
#### Results of GitLab environment info
<details>
<summary>Expand for output related to GitLab environment info</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)
</pre>
</details>
#### Results of GitLab application Check
<details>
<summary>Expand for output related to the GitLab application check</summary>
<pre>
(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:check SANITIZE=true`)
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true`)
(we will only investigate if the tests are passing)
</pre>
</details>
### Possible fixes
When the kubernetes runner displays the image, it does not consider the ENV variables. https://gitlab.com/gitlab-org/gitlab-runner/-/blob/master/executors/kubernetes/kubernetes.go#L186
The docker runner does: https://gitlab.com/gitlab-org/gitlab-runner/-/blob/9c9292b267a3132c41075ac09b968f3b5499ca68/executors/docker/docker.go#L1136
https://gitlab.com/gitlab-org/gitlab-runner/-/blob/9c9292b267a3132c41075ac09b968f3b5499ca68/executors/docker/docker.go#L952
issue