go.mod: bump sigs.k8s.io/controller-runtime to v0.23.3

PR #20388 (commit ca9f6971e) bumped k8s.io/* from v0.34 to v0.35 as a
transitive effect of pulling in helm v3.21 (for containerd CVE fixes).
The old controller-runtime v0.19.4 is aligned with k8s 1.31 APIs and
regresses at runtime against v0.35 client-go (informer reflectors stall
on Watch responses), leaving the operator unable to reconcile.

v0.23.3 is the release aligned with k8s.io/* v0.35 / Kubernetes 1.35.
The operator uses a narrow slice of controller-runtime (manager +
builder + client + reconcile + handler + source), so this bump is a
lift-and-shift: no reconciler wiring changes needed.

Test scaffolding fix: controller-runtime v0.20+ populates TypeMeta
(Kind/APIVersion) on objects returned by the fake client. The shared
expectEqual helper now strips TypeMeta before diffing so existing
tests continue to work without needing every 'want' object updated.

Tested: deployed to live clusters across Kubernetes 1.33, 1.34, 1.35,
and 1.36 (identical build per cluster). Verified the operator starts and
reconciles cleanly on all versions with no RBAC/forbidden errors, CRDs
establish and enforce validation, and the field indexers resolve
correctly under annotation churn (no stale-index misrouting). Exercised
the Service, ProxyClass, Connector, egress (simple + ProxyGroup, incl.
the EndpointSlice reconciler), and HA ingress-for-pg reconcilers.
Confirmed informer/watch recovery after an API server restart forces a
re-list/re-watch (the exact regression this bump fixes).

Updates tailscale/corp#44898

Signed-off-by: chaosinthecrd <tom@tmlabs.co.uk>