We don't perform any verification on the run-on-projects values

In at least two cases, we had some issues which were undetected.
bug 1627424 & https://bugzilla.mozilla.org/show_bug.cgi?id=1638260#c8

This is in-part a followup to 1638260 which fixed some cases of this problem.

Backed out 3 changesets (bug 1640278) for verify lint failure

Push with failure: https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel%2Crunning%2Cpending%2Crunnable&fromchange=dbf1e5788c2210c72006d77a5a840a3dd41afa2f&tochange=c6b49f0f97d9c60764ee20231589387b92c6adf3&selectedTaskRun=SDnJT8TyTJWTKv4Daz-krQ-0

Backout link: https://hg.mozilla.org/integration/autoland/rev/c6b49f0f97d9c60764ee20231589387b92c6adf3

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=305260120&repo=autoland&lineNumber=116

[task 2020-06-05T19:52:31.008Z] 19:52:31.8 flake8 (101) | Command: --config /builds/worker/checkouts/gecko/.flake8 --output-file /tmp/tmp5h6kir10 --format {"path":"%(path)s","lineno":%(row)s,"column":%(col)s,"rule":"%(code)s","message":"%(text)s"} --filename *.configure,*.py
[task 2020-06-05T19:52:43.150Z] 19:52:43.149 flake8 (102) | Finished in 12.36 seconds
[task 2020-06-05T19:52:56.923Z] 19:52:56.923 flake8 (104) | Finished in 26.13 seconds
[task 2020-06-05T19:53:31.363Z] 19:53:31.363 flake8 (103) | Finished in 60.57 seconds
[task 2020-06-05T19:53:36.072Z] 19:53:36.72 flake8 (101) | Finished in 65.28 seconds
[task 2020-06-05T19:53:36.079Z] TEST-UNEXPECTED-ERROR | /builds/worker/checkouts/gecko/taskcluster/taskgraph/util/verify.py:368:11 | multiple spaces after keyword (E271)
[taskcluster 2020-06-05 19:53:36.361Z] === Task Finished ===
[taskcluster 2020-06-05 19:53:37.029Z] Unsuccessful task run with exit code: 1 completed in 92.941 seconds

Depends on D76746

This could go further and test for m-c or the trunk/integration aliases, etc. but I opted for not letting this increase try-syntax jobs.

Depends on D81755

https://hg.mozilla.org/mozilla-central/rev/aabff19fe35d
https://hg.mozilla.org/mozilla-central/rev/31f6b0405b11
https://hg.mozilla.org/mozilla-central/rev/1a9f74ca35af
https://hg.mozilla.org/mozilla-central/rev/9898f1958c7c