Re-enable blur-cube-with-the-effect-renderer validation test

[bkaradzic-microsoft]

Re-enable blur-cube-with-the-effect-renderer validation test

What

Removes the excludeFromAutomaticTesting flag from the
blur-cube-with-the-effect-renderer Playground validation test
(Apps/Playground/Scripts/config.json) so it runs in the automatic suite again.

Why

The test renders an EffectRenderer / EffectWrapper fullscreen pass and used to
produce an all-black frame on Babylon Native, failing the pixel comparison. Root cause
was in the native engine: EffectRenderer disables depth testing through
engine.depthCullingState.depthTest = false, but the native engine only honored depth
state set via the explicit setDepthBuffer() command and never flushed
depthCullingState at draw time (unlike the WebGL/WebGPU applyStates() path). The
fullscreen quad therefore kept the previous draw's depth test and every fragment was
discarded.

Fixed upstream in the native engine:

• Babylon.js PR: [Native] Honor depthCullingState.depthTest on the native engine Babylon.js#18558 (branch native-honor-depthcullingstate-depthtest)

Depends on the above Babylon.js fix being released and the babylonjs dependency bumped
to a version that contains it. Until then this PR is a draft — CI will only pass once the
updated dependency is in place. (Verified locally against a patched native engine: see
below.)

Verification (local, against the patched native engine)

• blur-cube-with-the-effect-renderer now runs through the normal path (no
  --include-excluded) and passes:
  Test 'blur-cube-with-the-effect-renderer' validated.
• Full standard validation sweep: ran=274 passed=274 failed=0 — no regressions, and the
  re-enabled test is included.
• Scope check: this is the only excluded validation test fixed by the native-engine change
  (the other EffectWrapper-based excluded tests — the Atmosphere * set — still fail for
  unrelated reasons and remain excluded).