Add support for Python 3.12

[wosc]

The imp module has been removed in 3.12, replacing it with types.ModuleType was taken from pallets/flask@2de525c

[jensens]

I run into the Python 3.12 compatibility problem and can confirm this PR fixes the problem.

[jensens]

@icemac Is this package is still maintained? This PR would be important to get merged and released.
CI needs fixing too.
To pass the burden this could be moved (or forked under a different name) to zope or plone organizations if this helps.

/cc @gotcha

[icemac]

@jensens This package is still maintained, but it seems to be a good idea to move it to zopefoundation and maybe rename it to zope.pytestlayer.

I can do the move and integrate it into the workflow there.

[gotcha]

@icemac Would be great. This is a piece of software I am proud having been part of.

[icemac]

I moved gocept.pytestlayer to zope.pytestlayer and integrated into meta/config, see #44. But there are some problems due to pytest >= 8 there. Any help would be appreciated.

[icemac]

Superseded by #46.