fix: use displayTargetFile if targetFile is missing

[aarlaud]

• [x] Tests written and linted ℹ︎
• [x] Documentation written ℹ︎
• [x] Commit history is tidy ℹ︎

What this does

Uses displayTargetFile is targetFile is not in the snyk test json output.

[aarlaud]

:tada: This PR is included in version 1.2.1 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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