[DO NOT MERGE] Make screenshot error notification PendingIntent immutable am: 1eecc874b6

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/13519315

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I58a4ced63c067522eed4015eaef82e155ca2e119