don’t count tasks that are not defined as list items correctly

What does this MR do?

It fixes a problem with tasks counts: Tasks that are not formatted as list items are not considered as tasks (task_list gem requires that tasks are always in a list) however on our side we count these "not tasks" as tasks.

Reason

The regex that was used on our side is the same regex that is used in the task_list gem. However in that gem html string is being matched on the other hand in taskable.rb on our side we match simple text not the html version.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

bug reported in #26068 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

fixes #26068 (closed)