Backport of CSI: no early return when feasibility check fails on eligible nodes into release/1.2.x

[hc-github-team-nomad-core]

Backport

This PR is auto-generated from #13274 to be assessed for backporting due to the inclusion of the label backport/1.2.x.

The below text is copied from the body of the original PR.

---

Fixes #11778

As a performance optimization in the scheduler, feasibility checks
that apply to an entire class are only checked once for all nodes of
that class. Other feasibility checks are "available" checks because
they rely on more ephemeral characteristics and don't contribute to
the hash for the node class. This currently includes only CSI.

We have a separate fast path for "available" checks when the node has
already been marked eligible on the basis of class. This fast path has
a bug where it returns early rather than continuing the loop. This
causes the entire task group to be rejected.

Fix the bug by not returning early in the fast path and instead jump
to the top of the loop like all the other code paths in this method.
Includes a new test exercising topology at whole-scheduler level and a
fix for an existing test that should've caught this previously.

---

Note that the test here is potentially limited in reliability because of the random iterator, but:

$ go test -v ./scheduler -run TestServiceSched_CSITopology -count=100
...
--- PASS: TestServiceSched_CSITopology (0.00s)
PASS
ok      github.com/hashicorp/nomad/scheduler    0.424s

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