Allow star(*) in scalar value of rubocop.yml

[ksss]

Problem

I would like to exclude files that are no longer supported by RuboCop, but star (*) cannot be used in path specifications. (e.g. "gems/activerecord/7.2/**/*.rbs")
Since the target includes many old versions of various Rails-related gems, listing all files individually increases maintenance costs.

Proposal

I propose allowing the use of * in path specifications.
The * character is currently disallowed due to security concerns, as it can be used for YAML aliasing. However, since YAML.safe_load is already in use and does not permit aliases, this particular concern seems to be already addressed.

To further safeguard against unintentionally enabling alias functionality after allowing *, we have also added a guard clause.

Ref

https://github.com/ruby/gem_rbs_collection/actions/runs/15153815288/job/42604695763?pr=863

Run ruby .github/workflows/pr_bot/strict_rubocop_config.rb
.github/workflows/pr_bot/strict_rubocop_config.rb:66:in `validate_rubocop_yml!': Invalid characters in gems/activerecord/.rubocop.yml:7:30. (InvalidCharacters)
    - "gems/activerecord/7.2/**/*.rbs"
                             ^

	from .github/workflows/pr_bot/strict_rubocop_config.rb:9[5](https://github.com/ruby/gem_rbs_collection/actions/runs/15153815288/job/42604695763?pr=863#step:4:6):in `block in <main>'
	from .github/workflows/pr_bot/strict_rubocop_config.rb:[8](https://github.com/ruby/gem_rbs_collection/actions/runs/15153815288/job/42604695763?pr=863#step:4:9)9:in `each'
	from .github/workflows/pr_bot/strict_rubocop_config.rb:89:in `<main>'

[github-actions]

@ksss Thanks for your contribution!

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See also: https://github.com/ruby/gem_rbs_collection/blob/main/docs/CONTRIBUTING.md

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---

You changed non-gem files.

@pocke, please review and approve the changes.

[pocke]

Looks good, thanks!