Add nuskos@ to PartitionAlloc OWNERS.

Change-Id: Ic636924d969f52d1839c11f2dd628b64bc4f25b9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7550196
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Takashi Sakamoto <tasak@google.com>
Commit-Queue: Stephen Nusko <nuskos@chromium.org>
Auto-Submit: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1580623}
NOKEYCHECK=True
GitOrigin-RevId: e68e712315223a01924f14d73f8d61bc408a3a8c