[FIX] Ensure pipeline variables are returned from the graph in an aggregate query

[alyssadai]

• Closes #348

Changes proposed in this pull request:

• added pipeline_name and pipeline_version to list of variables returned in the aggregate graph response
• updated API-side graph response handling to return pipeline info even in aggregate mode
• minor conditional rewriting for clearer logic

Note: In this case, some tests started failing after the graph response handling logic was updated, since the mocked aggregate response from the graph used in those tests no longer matched the expected format (good). However, we are not yet to write a test that would fail under the original bug conditions (bad), since this would require a graph with data to test against. See https://github.com/neurobagel/api/issues/283

Checklist

This section is for the PR reviewer

• [x] PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF], [MODEL], [DOC]) (see our Contributing Guidelines for more info)
• [x] PR has a label for the release changelog or skip-release (to be applied by maintainers only)
• [x] PR links to GitHub issue with mention Closes #XXXX
• [x] Tests pass
• [x] Checks pass

For new features:

• [ ] Tests have been added

For bug fixes:

• [ ] There is at least one test that would fail under the original bug conditions.

[coveralls]

Pull Request Test Coverage Report for Build 11266360515

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 95.507%

---

Totals
Change from base Build 11261813541:	0.1%
Covered Lines:	744
Relevant Lines:	779

---

💛 - Coveralls

[neurobagel-bot[bot]]

:rocket: PR was released in v0.4.0 :rocket: