`initial_shared_runners_registration_token` configuration is ignored
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### Summary
`gitlab/gitlab-ee:13.12.1-ee.0` is ignoring the configuration for `gitlab_rails['initial_shared_runners_registration_token'] `
### Steps to reproduce
**This works as expected:**
```
docker run --detach --rm \
--env GITLAB_OMNIBUS_CONFIG="gitlab_rails['initial_shared_runners_registration_token'] = 'runner-reg-token'; " \
--publish 8080:80 \
--name gitlab_13_11 \
gitlab/gitlab-ee:13.11.3-ee.0
```

**This does not work as expected**
```
docker run --detach --rm \
--env GITLAB_OMNIBUS_CONFIG="gitlab_rails['initial_shared_runners_registration_token'] = 'runner-reg-token'; " \
--publish 8090:80 \
--name gitlab_13_12 \
gitlab/gitlab-ee:13.12.1-ee.0
```

### Example Project
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### What is the current *bug* behavior?
The token is generated randomly, ignoring the configuration.
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### What is the expected *correct* behavior?
The token is generated as per the configuration
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### Relevant logs and/or screenshots
See _Steps to reproduce_
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### Possible fixes
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issue