What

Fixes #3678
Fixes the three code smells called out in #3678 by introducing a Tracker
struct (shape b from the issue) that owns the three reference sets and
accumulates them via receiver methods.

Changes

pkg/k8s/deployer.go

• Add References struct holding Secrets, ConfigMaps, PVCs as
  sets.Set[string] values (not pointers — maps are already reference types).
• Add Tracker struct embedding References and NewTracker() constructor
  that initialises all three sets.
• Convert ProcessEnvs, ProcessVolumes, createEnvFromSource,
  createEnvVarSource from free functions with *sets.Set[string]
  out-parameters to *Tracker methods that write directly into the receiver.
• Update generateDeployment to accept *Tracker instead of three pointer
  parameters.
• Update CheckResourcesArePresent to accept References by value instead of
  three *sets.Set[string] parameters.
• Update both call sites in Deploy() (create and update paths).

pkg/knative/deployer.go

• Update generateNewService signature to accept *k8s.Tracker.
• Update both call sites in Deploy() (create and update paths).
• Remove now-unused sets import.

pkg/k8s/deployer_test.go / pkg/knative/deployer_test.go

• Replace three-variable sets.New[string]() + pointer passing with
  NewTracker() in all affected tests.
• Update regression test assertions to use tracker.Secrets /
  tracker.ConfigMaps.
• Remove unused sets imports.

Why shape (b) — Tracker receiver

• Structurally prevents the fix: apply resource validation to first-deploy path in k8s and keda deployers #3671 bug class. With out-parameters a caller
  can silently create a disconnected set and pass it alongside the one that
  gets validated; with a single Tracker receiver there is nothing to
  disconnect.
• Eliminates the pointer-to-map double-indirection. sets.Set[string] is
  map[string]Empty; passing it by value inside References already lets
  callees mutate the same backing store without the extra *.
• One argument instead of three at every call site.

Behavior

No behavior changes. This is a pure shape refactor.

Test plan

• go test ./pkg/k8s/ ./pkg/knative/ — both pass
• make check — 0 lint issues
• make test — all pre-existing unit tests pass