Reduce kubetest2 parallel tests

[saikat-royc]

What type of PR is this?

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/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:
Reduce kubetest2 ginkgo parallelism until #789 is resolved.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: saikat-royc

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[saikat-royc]

/hold

[k8s-ci-robot]

@saikat-royc: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-gcp-compute-persistent-disk-csi-driver-kubernetes-integration	a088763	link	/test pull-gcp-compute-persistent-disk-csi-driver-kubernetes-integration

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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