Set mac-osx-beta-rel trybot mb config

Copying mac-rel.

R=jbudorick

Bug: 999206
Change-Id: I7fb9ba2c0059b2a08db42fb0bcd39bd435fc2d6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1803896Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696471}

tools/mb/mb_config.pyl

@@ -841,6 +841,7 @@
       'ios-simulator-cronet': 'ios_error',
       'ios-simulator-xcode-clang': 'ios_error',
       'mac-jumbo-rel': 'jumbo_large_chunks_release_bot_compile_only',
+      'mac-osxbeta-rel': 'gpu_tests_release_trybot_deterministic_mac',
       'mac_chromium_10.10': 'gpu_tests_release_trybot_deterministic_mac',
       'mac_chromium_10.12_rel_ng': 'gpu_tests_release_trybot_deterministic_mac',
       'mac_chromium_10.13_rel_ng': 'release_trybot',