[3.18] Fix PyGObject requirements and deps

[pedro-psb]

I was working on a fix for 3.18 failures but got stuck with wrong response code errors (here). As this error doesnt seem related to the pygobject one, I'll submit that separately here, so we have some progress.

• PyGObject upperbound was updated because there is no 3.46.* public release, which would give errors with upperound constrains: Edge case error with calculated constrains plugin_template#897
• libgirepository1.0-dev was specifically requested by pip
• gir1.2-modulemd-2.0 fixed this error (ValueError: Namespace Modulemd not available, from gi package)

[noissue]

[mdellweg]

It seems like we do not install pygobject with pip (i can only assume it's preinstalled from rpm).
And any upper bound whatsoever will conflict with the upper bounds constraints.
At this point i think we need to exempt this library from the bounds calculator altogether. This also sadly means we never test any version other than the one provided in the image.

[pedro-psb]

@ggainey I've manually applied the latest plugin-template so we can see that the pygobject errors are gone.

Now we are left with the "403 instead of 405 error", but I dont see any evidence that these two are correlated.
Can we merge this so we can work out the 405 independently?

[ggainey]

The one failing test needs investigation - but it doesn't appear to be caused by the changes happening here to get us building again in this (suported) channel. Approving, so we can get a little further, and separate the two issues.