Repeat HTTP 500 errors when checking upstream repos

[sentry]

Sentry Issue: UPDATEBOT-PROD-3C

CalledProcessError: Command '['./mach', 'vendor', '--check-for-update', 'js/src/irregexp/moz.yaml']' returned non-zero exit status 1.
(3 additional frame(s) were not displayed)
...
  File "components/utilities.py", line 161, in wrapper
    return func(*args, **call_kwargs)
  File "components/mach_vendor.py", line 26, in check_for_update
    result = self.run(["./mach", "vendor", "--check-for-update", library.yaml_path]).stdout.decode().strip()
  File "components/commandprovider.py", line 24, in run
    return _run(args, shell=shell, clean_return=clean_return,
  File "components/commandrunner.py", line 86, in _run
    ret.check_returncode()
  File "subprocess.py", line 502, in check_returncode
    raise CalledProcessError(self.returncode, self.args, self.stdout,

[mozfreddyb]

This could be a P1 if it comes up again. I'm guessing we might be hitting WAFs or such by issuing requests like to API paths like https://aomedia.googlesource.com/aom/+/HEAD?format=JSON.

An alternative way to check for new revisions could be to directly check out and pull the code.