Revert removal of roubert@google.com from OWNERS.

This partially reverts commit a903cc7, the bug that required this entry
to be removed then has been fixed now:

https://gerrit.googlesource.com/plugins/find-owners/+/7a4ec6a

Bug: 79676796
Test: repo upload
Change-Id: Ideda071d5262bee8e4376f292e4b1fb9db2c37d9
1 file changed