[GraphBolt] Edge feature fetch fix.

[mfbalin]

Description

The modified test fails. In this PR, I plan to fix it by always enabling return_eids=True when sampling.

EDIT: Looks like edge feature fetch was broken all this time. Our tests do actually cover it but assertions were not written to check for it.

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• I've leverage the tools to beautify the python and c++ code.
• The PR is complete and small, read the Google eng practice (CL equals to PR) to understand more about small PR. In DGL, we consider PRs with less than 200 lines of core code change are small (example, test and documentation could be exempted).
• All changes have test coverage
• Code is well-documented
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
• Related issue is referred in this PR
• If the PR is for a new model/paper, I've updated the example index here.

Changes

[dgl-bot]

To trigger regression tests:

• @dgl-bot run [instance-type] [which tests] [compare-with-branch];
  For example: @dgl-bot run g4dn.4xlarge all dmlc/master or @dgl-bot run c5.9xlarge kernel,api dmlc/master

[dgl-bot]

Commit ID: 140aa39

Build ID: 1

Status: ⚪️ CI test cancelled due to overrun.

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[dgl-bot]

Commit ID: 47e0080

Build ID: 2

Status: ❌ CI test failed in Stage [Lint Check].

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[dgl-bot]

Commit ID: c8978a7

Build ID: 4

Status: ❌ CI test failed in Stage [Torch CPU (Win64) Unit test].

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[dgl-bot]

Commit ID: 17f1b8c

Build ID: 5

Status: ❌ CI test failed in Stage [Torch CPU (Win64) Unit test].

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[dgl-bot]

Commit ID: fff2b24

Build ID: 6

Status: ❌ CI test failed in Stage [Torch CPU (Win64) Unit test].

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[dgl-bot]

Commit ID: 6ee6d49

Build ID: 7

Status: ⚪️ CI test cancelled due to overrun.

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[dgl-bot]

Commit ID: b32cfa3

Build ID: 8

Status: ❌ CI test failed in Stage [Torch CPU (Win64) Unit test].

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Full logs path: link

[dgl-bot]

Commit ID: c9e2c08

Build ID: 9

Status: ✅ CI test succeeded.

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[mfbalin]

The distributed tests run successfully on my local @Rhett-Ying

[frozenbugs]

I am confused by this PR, why always enabling return_eids=True when sampling?

[mfbalin]

I am confused by this PR, why always enabling return_eids=True when sampling?

#7589 (comment)