Clear host memoization for metric embeds feature test

What does this MR do?

!24601 (merged) introduced memoization for regex matchers in Gitlab::Metrics::Dashboard::Url.

If you run spec/features/markdown/metrics_spec.rb before or after another test which depends on these regexes, the latter test file will have failures, as metrics_spec.rb configures a host other than localhost.

This MR:

• Clears the memoization before and after the metrics_spec.rb runs to avoid leaking state to other specs
• Changes some spacing which was bothering me
• Updates a spec description to match the corresponding method name which was also changed in !24601 (merged)

Testing

Example of tests which can be run to see the failures & validate the solution: rspec spec/features/markdown/metrics_spec.rb spec/lib/banzai/filter/inline_metrics_redactor_filter_spec.rb

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done