fix(tableau): assert error on parent name

[sgomezvillamor]

While Site Administrator Explorer privileges are required, users occasionally need to operate with a lower level of privileges. If so, the following error is thrown:

File "/tmp/datahub/ingest/venv-tableau-bac61a203a4fea43/lib/python3.10/site-packages/datahub/ingestion/source/tableau/tableau.py", line 3405, in emit_project_in_topological_order
assert (
AssertionError: project Customer First should not be null

This occurs because the Tableau API returns partial information when listing projects: child projects might include a reference to the parent project id, but the listing omits those projects that the credentials aren't allowed to access. As a result, the ingestor cannot perform the project name enrichment for such a parent project ID.

In this PR, when this happens, we remove the reference to the parent project from the child. This allows us to provide at least partial but functional information.

Checklist

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...on/src/datahub/ingestion/source/tableau/tableau.py	66.66%	2 Missing ⚠️

Files with missing lines	Coverage Δ
...on/src/datahub/ingestion/source/tableau/tableau.py	89.12% <66.66%> (+0.01%)	⬆️

... and 3 files with indirect coverage changes

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[hsheth2]

maybe just add a comment that this indexing is safe based on the guarantees provided by fetch_projects

[sgomezvillamor]

I added the assert a few lines above with that specific purpose