[GraphBolt] Fix NegativeSampler seeds support.

[yxy235]

Description

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: 4353899

Build ID: 1

Status: ❌ CI test failed in Stage [Torch CPU Example test].

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[yxy235]

@dgl-bot

[dgl-bot]

Commit ID: c788ef61ed4f195f5eb151102b0b5d33c6731402

Build ID: 2

Status: ✅ CI test succeeded.

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Full logs path: link

[dgl-bot]

Commit ID: 76d753f91ec8027d4c739a76c94eccf274721354

Build ID: 3

Status: ⚪️ CI test cancelled due to overrun.

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Full logs path: link

[dgl-bot]

Commit ID: 872eb9d0192a7cf180fa4faf8e404d150662fada

Build ID: 4

Status: ✅ CI test succeeded.

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