Disable Python 3 for GRIT presubmit

This CL disabled the Python 3 version of the GRIT presubmit as it causes
bots to hang when running test_suite_all.py.

Bug: 1145395

Change-Id: I90426733f40496a97a029d79e83cb0a91945bb37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518306
Auto-Submit: calamity <calamity@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/master@{#825583}

tools/grit/PRESUBMIT.py

@@ -11,11 +11,14 @@ details on the presubmit API built into gcl.
 
 def RunUnittests(input_api, output_api):
   presubmit_path = input_api.PresubmitLocalPath()
-  return input_api.canned_checks.RunUnitTests(input_api, output_api, [
-      input_api.os_path.join('grit', 'test_suite_all.py'),
-      input_api.os_path.join(input_api.PresubmitLocalPath(),
-                             'preprocess_grit_test.py')
-  ])
+  return input_api.canned_checks.RunUnitTests(
+      input_api,
+      output_api, [
+          input_api.os_path.join('grit', 'test_suite_all.py'),
+          input_api.os_path.join(input_api.PresubmitLocalPath(),
+                                 'preprocess_grit_test.py')
+      ],
+      run_on_python3=False)  # See https://crbug.com/1145395.
 
 
 def CheckChangeOnUpload(input_api, output_api):