Add SEND_SAFETY_CENTER_UPDATE to shell permissions.

This is to ensure the CTS tests SafetyCenterManagerTest still passes
after enforcing the permission.
Test: atest CtsSafetyCenterTestCases
Bug: 205706756
Ignore-AOSP-First: Not announced yet, and need to use a permission
that hasn't been merged in AOSP

Change-Id: Iaee11c55fc25a82299d4c45dd7d24151a4f8c30b