Re-opened the bug since I managed to repro on 2021.2.10f1.

Basically the repro steps are simple, just not 100% of the time:
- Retrieve the project
- Open Profiler, under profiling modules, add GPU usage
- Select the new GPU section
- Here search for MotionBlur pass
- Press Play
- Enable / Disable DLSS and see the 5 folds increase of the GPU cost of the pass.

Additional info:
- If does not happen, quit turn unity off and on again.
- Does not seems to happen with other DRS filters.

It also happens on different passes like LensFlareDataDriven / Bloom as per user reports.

Forum thread: https://forum.unity.com/threads/dlss-increases-motion-blur-other-perf-costs-by-over-5x.1206709/

Also, it reproes on trunk as well.