Fix Web Help showing up on custom classes (and maybe elsewhere) when it shouldn't

[CAM-Gerlach]

@martinRenou Looks like our visual regression tests just started failing on the Class Sphinx test on all platforms, presumably due to a dep update in the CIs in the past 24 hours, "Web Help" is being mistakenly shown when I presume it shouldn't, given custom toy classes certainly don't have it. I've seen this elsewhere on some other cases; I presume the code that detects whether web help is available (AFAIK, just for stdlib code?) is rather buggy? I can look into it, but I appreciate your help too, and this would be a good chance to test out the bot in a real-world setting.