test: add failing test for multiple JSON output

[snyk-tim]

Summary

This PR adds a failing test that demonstrates an issue where only the first workflow.Data item is output when multiple items with application/json content type are passed to the output workflow with --json flag.

Question for the team: Is this intended behavior, or should multiple JSON items be output?

Problem

When a workflow returns multiple workflow.Data items (e.g., scanning multiple lock files), only the first JSON result is printed to stdout. All subsequent results are silently dropped.

Expectation

When encountering multiple workflow.Data they should all be output with the correct renderer. In this case with application/json I would expect the output to be JSONL/NDJSON. One line per JSON separated by a \n character.

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[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scanner	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

💻 Catch issues earlier using the plugins for VS Code, JetBrains IDEs, Visual Studio, and Eclipse.