Disable E2E DP test unless nightly

[wenxindongwork]

Description

Currently we are running the DP e2e test for every build, this PR sets this test to trigger only in nightly runs.

Tests

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commands to reproduce.

Checklist

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• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have made or will make corresponding changes to any relevant documentation.

[github-actions]

Description

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the past.

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Tests

Please describe how you tested this change, and include any instructions and/or
commands to reproduce.

Checklist

Before submitting this PR, please make sure:

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have made or will make corresponding changes to any relevant documentation.

[QiliangCui]

I would suggest don't disable it for now.

1. this is new feature and we should keep close monitor.
2. the latest run shows 1 min waiting and 9 minutes of running, which is not bad.
3. b/457722504 works on increasing v6e-8 capacity.

I think no need to disable before seeing any blocking issue.