[DanglingPointer] Remove dangling pointer in

ukm_manager_unittest.cc

Bug: 1291138
Change-Id: I609c40c58d2d96a410f95fbc7fc81c507319f26a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5076197


Commit-Queue: Shubham Gupta <shubham.gupta@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Shubham Gupta <shubham.gupta@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1234041}