Refactor Ci::Build#group_name [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

This merge request removes matrix brackets : [...] and parallelization digits X Y / X/Y / X\Y from the end of build names only before grouping, leaving prefix and infix matches intact.

Examples

See the new specs added for the changes, they are most of the previously used pairs but with some changes.

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