fix(security_scanning): Improve fetching security report results

Description

Fixes some edge cases that would cause the findings to show 0 results.

What this MR changes

See plan from #1255 (closed)

Additional tests

I opted for integration level tests that is inclusive of the mergeReports function. I think would have been a pain to unit test all the helper functions I added, when we have better coverage with the integration level tests that tie it all together. ( call to getSecurityReports w/ mocked network requests)

The scenarios in #1255 (closed) are covered with integration level tests.

Related Issues

Resolves #1255 (closed)

How has this been tested?

• Pull this branch, and launch vs-code workflow extension
• Look for a recently completed and successful pipeline run https://gitlab.com/gitlab-org/gitlab/-/pipelines?page=8&scope=finished&status=success
• Checkout that branch.
• Observe either the results parsing, or the results showing immediately (depends on if the results are cached on the gitlab server)

Screenshots (if appropriate)

Before	After

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap

Closes #1255 (closed)