Update OWNERS for core/java/android/security

Update the OWNERS file for core/java/android/security:
* Bernardo is no longer reviewing changes to files in this directory
  (confirmed with him via chat).
* This file covers multiple Keystore Java source files, so adding myself
  as an owner.

Bug: 323132824
Test: N/A
Change-Id: I93e25a2794671b03bcb183fb9b472e6f01d34254