Add chrome-screen-ai-releaser@ to KNOWN_ROBOTS in PRESUBMIT.py

Add the chrome-screen-ai-releaser service account email to KNOWN_ROBOTS
so that the presubmits don't think that this is an external account
trying to commit to src.

Note that chrome-screen-ai-releaser is currently configured to create a
Gerrit CL that updates the screen-ai CIPD instances in //DEPS when it
builds and releases the ScreenAI library from Google3 to Chromium
bi-weekly.

AX-Relnotes: n/a.
Bug: b:281483558, b:330070850
Test: python3 PRESUBMIT_test.py
Test: crrev.com/c/5388533 created by the chrome-screen-ai-releaser bot passes the presubmits after being rebased on this CL.
Change-Id: I68176effdba4033586bc6fb73e80010de1b1d1e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5415498


Commit-Queue: Kyungjun Lee <kyungjunlee@google.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1281561}