Fixed copy contents functionality for snippets

What does this MR do?

Fixes the "Copy Content" functionality for snippets with multiple files.

Screenshots (strongly suggested)

Before	After
Snippet-copy-bug-before	Snippet-copy-bug-after

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

References #276913 (closed)