Fix issue where deleting a workspace deletes the PVC incorrectly

[amisevsk]

What does this PR do?

Fix a regression caused by commit cbd3fd1. When deleting workspaces, if
there are no non-terminating workspaces left in the namespace, we delete
the common PVC rather than running cleanup jobs. However, the way the
check was written assumed that we were counting all workspaces, and
would delete the common PVC if there were two workspaces in a namespace
and one was deleted.

What issues does this PR fix or reference?

Mentioned in review for #846 (review) -- I'm not sure how I didn't catch it in the original PR; test case was likely missed by me testing

• delete a single workspace
• delete 3-5 workspaces at once

Closes#871

Is it tested? How?

kubectl apply -f samples/theia-next.yaml
yq '.metadata.name="theia-next-2"' samples/theia-next.yaml | kubectl apply -f -
# wait for workspaces to enter running state
kubectl delete dw theia-next
kubectl get pvc # should not be terminating.

PR Checklist

• E2E tests pass (when PR is ready, comment /test v8-devworkspace-operator-e2e, v8-che-happy-path to trigger)
  • v8-devworkspace-operator-e2e: DevWorkspace e2e test
  • v8-che-happy-path: Happy path for verification integration with Che

[amisevsk]

Once merged, this PR should be cherry-picked to the 0.15.x branch.

[AObuchow]

This fixes the issue that the PR aims to fix, but prevents the PVC from being deleted when there are no workspaces present (
i.e. delete both workspaces and see that the common PVC is not deleted). I'm going to think a bit more of another potential fix.

[amisevsk]

@AObuchow I had made a mistake (>= 0 vs > 0) -- should be fixed now.

[AObuchow]

@amisevsk Works as expected now :)

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: amisevsk, AObuchow, ibuziuk

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