Add GitHub checks summary to all Taskcluster tasks

[stephenmcgruer]

#15412 oversaw the addition of GitHub checks output to the major Taskcluster checks (stability and lint). This issue exists to track the other tasks, which are less important but could still do with some improvements:

• sink-task : requires both clearer documentation and could also link directly to the actually-failing tasks.
• update-built: probably best to just log the diff if non-empty.
• tools/ unittests (Py2, Py3.6, and Py3.8 variants): pytests, so difficult to hook into.
• tools/ integration tests (Py2, Py3.6, and Py3.8 variants): pytests, so difficult to hook into.
• resources/ tests: pytests, so difficult to hook into.
• infrastructure/ tests (plus Python 3 variant): executes a wpt run via ./tools/ci/ci_wptrunner_infrastructure.sh; the best documentation would be difficult to get as it would be the list of failed tests from the wpt logs.

(I've probably missed some)

The other checks don't tend to indicate success or failure, they are just things like results with/without (which exist to fuel wpt.fyi results which are recorded separately).