update-built tests failing on PRs

[foolip]

Two examples:
#31223
#31230

From one of the logs:

+ .virtualenv/bin/python gentest.py
Traceback (most recent call last):
  File "gentest.py", line 3, in <module>
    genTestUtils('../element', '../element', 'templates.yaml', 'name2dir.yaml', False)
  File "/home/test/web-platform-tests/html/canvas/tools/gentestutils.py", line 123, in genTestUtils
    templates = yaml.load(open(TEMPLATEFILE, "r").read())
TypeError: load() missing 1 required positional argument: 'Loader'

This is probably a regression that landed in master. I'm filing this now without further investigation and don't have time to look closer right now.

cc @web-platform-tests/wpt-core-team

[Ms2ger]

Probably this bug in yesterday's release: yaml/pyyaml#576

https://github.com/web-platform-tests/wpt/blob/7b0ebaccc62b566a1965396e5be7bb2bc06f841f/html/canvas/tools/build.sh doesn't pin the version

[Ms2ger]

(We might wanna switch to safe_load anyway, even though input is trusted.)