Update Shared Highlight Component OWNERS

Adding myself.

Change-Id: Icf1d531b025188f8a512bcb97e12c965801c8d37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495054
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Commit-Queue: sebsg <sebsg@chromium.org>
Auto-Submit: Sebastien Lalancette <seblalancette@chromium.org>
Reviewed-by: sebsg <sebsg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820415}

components/shared_highlighting/OWNERS

 sebsg@chromium.org
+seblalancette@chromium.org
 
 # COMPONENT: UI>Browser>SharedHighlighting
 # TEAM: chrome-shared-highlighting@google.com
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