Replace constant with string literals in streaming audit events specs

The following discussion from !128313 (merged) should be addressed:

• @ealcantara started a discussion: (+1 comment)

  suggestion Could we replace this constant with the string literal? We recently documented a guideline that recommends using string literals in tests: https://docs.gitlab.com/ee/development/i18n/externalization.html#test-files-jest. The documentation explains the reasoning behind this recommendation.

            'Destination Name',