Verify WantDeleteCollections in TableTest

[pujitha24]

Fixes #2455

Motivation:
TableRow.WantDeleteCollections has existed since it was added to the
struct, but (r *TableRow) Test() never compared it against the actual
recorded DeleteCollection actions. A test author setting
WantDeleteCollections gets no verification at all: whether the
reconciler under test issues the expected DeleteCollection call, issues
the wrong one, or issues none, the test silently passes either way.

A maintainer comment on the issue speculated this couldn't be fixed
because of an upstream fake-client limitation
(kubernetes/kubernetes#105357), where DeleteCollection calls with a
label selector don't actually remove matching objects from the fake
ObjectTracker. That bug is real, but it's orthogonal to this issue:
reconciler/testing/actions.go's ActionsByVerb() already captures
delete-collection verb actions into Actions.DeleteCollections from
the fake clientset's recorded action list, independent of whether the
tracker actually performed the deletion. So the missing verification in
Test() is a separate, fixable gap in the test framework itself, not
blocked by the upstream issue.

Approach:
Add a verification block in Test(), alongside the existing
WantDeletes check, that compares r.WantDeleteCollections against
actions.DeleteCollections. DeleteCollectionActionImpl has no
GetName() (it targets a namespace + label/field selector, not a single
named object), so it can't reuse the WantDeletes comparison verbatim.
Instead, a new deleteCollectionKey helper builds a comparison key from
resource + label selector string + field selector string (+ namespace,
unless SkipNamespaceValidation is set), and the two sets of keys are
compared the same way WantDeletes/gotDeletes are. Nil label/field
selectors (as would result from a hand-written
DeleteCollectionActionImpl{} literal in a test's
WantDeleteCollections) are treated as labels.Everything() /
fields.Everything(), matching what client-go's own
NewDeleteCollectionActionWithOptions defaults them to internally, so
constructing a "delete everything" expectation doesn't panic on a nil
selector's .String().

This does not change behavior for any existing test: a repo-wide search
found no existing use of WantDeleteCollections anywhere in
knative/pkg, since it was never actually verified before. It only turns
a previously-silent no-op field into a working one, so tests written
against it going forward actually enforce their expectations.

Validation:
go build ./...
go test ./reconciler/... -count=1
go test ./webhook/psbinding/... -count=1
both pass. Added reconciler/testing/table_test.go with
TestDeleteCollectionKey, unit-testing the new helper directly:
constructor-built vs. hand-written-literal actions key identically,
nil-selector defaults match an explicit "everything" selector, and
namespace affects the key unless SkipNamespaceValidation is set.

/kind bug

Signed-off-by: Pujitha Paladugu 10557236+pujitha24@users.noreply.github.com

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