Post-processing is not applied when Alpha Processing is enabled and Upscaling Filter is set to Spatial-Temporal Post-Processing

How to reproduce:

1. Open the attached “IN-151800” project
2. Open the “STPBug” scene
3. In the Project tab, select the “PC_RPAsset.asset”
4. In the Inspector tab, expand “Quality”
5. Under the “Quality”, disable “HDR” option
6. Under the “Quality”, set “Upscaling Filter” to “Spatial-Temporal Post-Processing”
7. In the Inspector tab, expand “Post-processing”
8. Under the “Post-processing”, enable “Alpha Processing”
9. Observe the result in the Game view

Actual result: No post-processing is applied - the sky renders as the default blue skybox and no vignette is visible
Expected result: Post-processing is applied - the sky is green and the vignette is visible

Reproducible with: 6000.0.1f1, 6000.0.82f1, 6000.3.23f1, 6000.5.10f1, 6000.6.0b10, 6000.7.0a5

Reproducible on: Windows 11 Enterprise (25H2)
Not reproducible on: No other environments tested

Note: The bug also reproduces when “HDR” option is enabled and “HDR Precision” is set to “64 Bits”