Fix Ruby compile time warning in gitlab runner QA spec

What does this MR do and why?

The following Ruby warning is now fixed:

42: warning: regular expression has redundant nested repeat operator '*': /--registration-token **** /

Refs !92841 (diffs, comment 1044719433)

How to set up and validate locally

Before

ruby -wc qa/spec/service/docker_run/gitlab_runner_spec.rb
qa/spec/service/docker_run/gitlab_runner_spec.rb:42: warning: regular expression has redundant nested repeat operator '*': /--registration-token **** /
qa/spec/service/docker_run/gitlab_runner_spec.rb:42: warning: regular expression has redundant nested repeat operator '*': /--registration-token **** /
qa/spec/service/docker_run/gitlab_runner_spec.rb:42: warning: regular expression has redundant nested repeat operator '*': /--registration-token **** /
Syntax OK

After

ruby -wc qa/spec/service/docker_run/gitlab_runner_spec.rb
Syntax OK

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