WPT tests runner Python error

[gterzian]

When I run ./mach test-wpt tests/wpt/web-platform-tests/fetch/http-cache

I get

File "/servo/tests/wpt/grouping_formatter.py", line 108, in suite_start
    self.number_of_tests = sum(len(tests) for tests in data["tests"].itervalues())
AttributeError: 'list' object has no attribute 'itervalues'

removing the call to itervalues at

servo/tests/wpt/grouping_formatter.py

Line 108 in e13f5a6

self.number_of_tests = sum(len(tests) for tests in data["tests"].itervalues())

fixed it for me locally. Seems like the data is now a list, and not a dict?

Is this worth a PR or I am just getting something wrong in my local setup?

[jdm]

It is definitely worth a PR.

[KiChjang]

Fixed in #18724.