Python error when reporting non-intermittent failures on mac

[jdm]

From https://community-tc.services.mozilla.com/tasks/B5l6bUP7Rsqe2TNtsAkKSQ/runs/0/logs/https%3A%2F%2Fcommunity-tc.services.mozilla.com%2Fapi%2Fqueue%2Fv1%2Ftask%2FB5l6bUP7Rsqe2TNtsAkKSQ%2Fruns%2F0%2Fartifacts%2Fpublic%2Flogs%2Flive.log

+ ./mach filter-intermittents wpt-jsonsummary.log --log-intermittents intermittents.log --log-filteredsummary filtered-wpt-errorsummary.log --tracker-api default --reporter-api default
Error running mach:
    ['filter-intermittents', 'wpt-jsonsummary.log', '--log-intermittents', 'intermittents.log', '--log-filteredsummary', 'filtered-wpt-errorsummary.log', '--tracker-api', 'default', '--reporter-api', 'default']
The error occurred in code that was called by the mach command. This is either
a bug in the called code itself or in the way that mach is calling it.
You should consider filing a bug for this issue.
If filing a bug, please include the full output of mach, including this error
message.
The details of the failure are as follows:
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2 in position 57: ordinal not in range(128)
  File "/Users/worker/tasks/task_1575999096/repo/python/servo/testing_commands.py", line 580, in filter_intermittents
    format(actual_failures, description)
  File "/Users/worker/tasks/task_1575999096/repo/python/servo/testing_commands.py", line 568, in format
    file.write(formatted.encode("utf-8"))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/codecs.py", line 357, in write
    data, consumed = self.encode(object, self.errors)

cc @SimonSapin

[SimonSapin]

Like before, the filtered-wpt-errorsummary.log artifacts contain the same information that the failing code would print. So we can look there until this is fixed.