Update OWNERS (istio#2049)

Automatic merge from submit-queue.

Update OWNERS

**What this PR does / why we need it**:

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
none
```

@mattdelco  FYI: https://github.com/istio/test-infra/tree/master/mungegithub#owners-file

release/OWNERS

@@ -2,3 +2,4 @@ approvers:
   - ldemailly
   - linsun
   - sebastienvas
+  - mattdelco