$ ./Tools/Scripts/wpt-export --gh-user=chromium-wpt-export-bot --gh-token=$TOKEN
WPT checkout exists at /tmp/wpt, fetching latest
Traceback (most recent call last):
  File "./Tools/Scripts/wpt-export", line 68, in <module>
    main()
  File "./Tools/Scripts/wpt-export", line 64, in main
    test_exporter.run()
  File "/Users/foolip/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_exporter.py", line 38, in run
    self.export_first_exportable_commit()
  File "/Users/foolip/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_exporter.py", line 65, in export_first_exportable_commit
    wpt_commit, chromium_commit = self.local_wpt.most_recent_chromium_commit()
  File "/Users/foolip/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/w3c/local_wpt.py", line 61, in most_recent_chromium_commit
    chromium_commit = ChromiumCommit(self.host, position=position)
  File "/Users/foolip/chromium/src/third_party/WebKit/Tools/Scripts/webkitpy/w3c/chromium_commit.py", line 35, in __init__
    assert len(sha) == 40, 'Expected SHA-1 hash, got {}'.format(sha)
AssertionError: Expected SHA-1 hash, got usage: git rev-list [OPTION] <commit-id>... [ -- paths... ]

The problem is inside git crrev-parse, and can be reproduced with:

$ git crrev-parse 'refs/heads/master@{#450889}'

The $remote_ref variable gets the value refs\/remotes\/origin/master with extra backslashes, so presumably there's something fun about escaping working differently in macOS's old bash going on.