Fireflies are visible when using baked/mixed punctual lights

Steps to reproduce:

1. Download and open the attached project (Fireflies-Bug.zip)
2. Open SampleScene
3. Navigate to Lighting window (Window > Rendering > Lighting)
4. Make sure that Filtering field is set to None
5. Generate lighting
6. Observe the noise/fireflies

Notes:

• Reproduces in URP and HDRP by default; reproduces in BiRP when using custom light falloff scripts
• Reproduces in all Unity editor versions
• Reproduces both with CPU and GPU lightmappers
• Fireflies eventually go away when using really high sample counts; this extends bake times considerably