Pin the scheduler-plugins version

[tenzen-y]

What this PR does / why we need it:
I pinned the scheduler-plugins version to fix CI errors.

Which issue(s) this PR fixes (optional, in Fixes #<issue number>, #<issue number>, ... format, will close the issue(s) when PR gets merged):
Ref #1769

Checklist:

• Docs included if any changes are user facing

[coveralls]

Pull Request Test Coverage Report for Build 4402988623

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 11 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.01%) to 39.368%

---

Files with Coverage Reduction	New Missed Lines	%
pkg/controller.v1/mpi/mpijob_controller.go	2	76.79%
pkg/controller.v1/pytorch/pytorchjob_controller.go	9	58.19%

Totals
Change from base Build 4206779468:	0.01%
Covered Lines:	2727
Relevant Lines:	6927

---

💛 - Coveralls

[johnugeorge]

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: johnugeorge, tenzen-y

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