Re-enable blur-cube-with-the-effect-renderer validation test (#1763)

## What

Re-enables the `blur-cube-with-the-effect-renderer` Playground
validation test (`#4C900K#2`) by
dropping its `excludeFromAutomaticTesting` entry in `config.json`, and
bumps the bundled `babylonjs`
to **9.15.0** (which contains the paired engine fix) so the test
actually passes in CI.

Two commits:
1. Re-enable `blur-cube-with-the-effect-renderer` in
`Apps/Playground/Scripts/config.json`.
2. Bump `babylonjs` to 9.15.0 in `Apps/package.json` +
`Apps/package-lock.json`.

Broken out of #1748 so it
can merge independently:
#1748 re-enables this same test alongside six single-file-`.dds` cube
tests, but those six are still
gated on an unmerged cube-loading TS change
(BabylonJS/Babylon.js#18567), whereas this test only
needs the already-merged depth-test fix. (#1748 currently still carries
a duplicate `blur-cube`
re-enable; that entry should be dropped there once this lands.)

## Why it passes now

The test previously failed pixel comparison because the native engine
ignored
`depthCullingState.depthTest`, so an `EffectRenderer` fullscreen pass
produced an all-black frame.
That is fixed by BabylonJS/Babylon.js#18558
("[Native] Honor
depthCullingState.depthTest on the native engine"), **merged 2026-06-16
and shipped in `babylonjs`
9.15.0** — the version this PR now pins. With that fix present in the
bundled engine the pass renders
correctly and the test matches its reference image.

## Status

- **Pin bump included; the earlier gate is resolved.** The bump to
9.15.0 (which contains #18558) is
part of this PR, so the re-enable no longer depends on a separate future
`babylonjs` bump.
- **CI is fully green**, including every Win32 D3D11 and Ubuntu desktop
job that runs the validation
suite — `blur-cube-with-the-effect-renderer` validates. Ready to merge
(pending review).

---------

Co-authored-by: Branimir Karadzic <branimirkaradzic@gmail.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Branimir Karadzic <bkaradzic@users.noreply.github.com>

Author: 3 people

Apps/Playground/Scripts/config.json

@@ -2575,8 +2575,6 @@
             "title": "blur-cube-with-the-effect-renderer",
             "playgroundId": "#4C900K#2",
             "renderCount": 20,
-            "excludeFromAutomaticTesting": true,
-            "reason": "Pixel comparison fails (more than 20% pixels differ)",
             "referenceImage": "blur-cube-with-the-effect-renderer.png"
         },
         {

Apps/package-lock.json

@@ -9,13 +9,13 @@
     "getNightly": "node scripts/getNightly.js"
   },
   "dependencies": {
-    "babylonjs": "^9.3.4",
-    "babylonjs-addons": "^9.3.4",
-    "babylonjs-gltf2interface": "^9.3.4",
-    "babylonjs-gui": "^9.3.4",
-    "babylonjs-loaders": "^9.3.4",
-    "babylonjs-materials": "^9.3.4",
-    "babylonjs-serializers": "^9.3.4",
+    "babylonjs": "^9.15.0",
+    "babylonjs-addons": "^9.15.0",
+    "babylonjs-gltf2interface": "^9.15.0",
+    "babylonjs-gui": "^9.15.0",
+    "babylonjs-loaders": "^9.15.0",
+    "babylonjs-materials": "^9.15.0",
+    "babylonjs-serializers": "^9.15.0",
     "jsc-android": "^241213.1.0",
     "v8-android": "^7.8.2"
   }