Fix param type for rspec args

What does this MR do and why?

The param type of rspec_args should be a string, not an Array<String (frozen)>.

Incompatible types
Required: String
Passed: Array<String (frozen)>

While the current format of this appears to work in ruby3.1 it seems that it may break when we bump to ruby3.2 as noted in #724

bundler: failed to load command: gitlab-qa (/builds/gitlab-org/gitlab/.gems/bin/gitlab-qa)
/builds/gitlab-org/gitlab/.gems/gems/gitlab-qa-14.9.0/lib/gitlab/qa/component/specs.rb:97:in `block in feature_flag_sets': undefined method `=~' for ["--tag", "integrations"]:Array (NoMethodError)

How to set up and validate locally

$ asdf shell ruby 3.1.5 
$ bundle install
$ bundle exec exe/gitlab-qa Test::Integration::Jira EE
# etc 

$ asdf shell ruby 3.2.3 
$ bundle install
$ bundle exec exe/gitlab-qa Test::Integration::Jira EE 
# etc 

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• Commits include Changelog: trailer
• I have evaluated the MR acceptance checklist for this MR.