Add Joanie to OWNERS files for desktop Linux accessibility

Bug: none
Change-Id: Iec4ac4ab0ae6a8b911fc0f9d807b34ed003e1e1d
Notry: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539862
Auto-Submit: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644381}

content/browser/accessibility/OWNERS

 file://ui/accessibility/OWNERS
 
 # For ATK / AuraLinux
+jdiggs@igalia.com
 mrobinson@igalia.com
 
 # TEAM: chromium-accessibility@chromium.org

ui/accessibility/platform/OWNERS

 # For ATK / AuraLinux
+jdiggs@igalia.com
 mrobinson@igalia.com