Summary

When the Ubuntu 22.04 (both x86 and ARM) test jobs currently run in GitHub Actions,girepository-1.0 is installed as a system dependency, andPyGObject is installed from PyPI without any version range specifier.

This causes thePyGObject Python package to fail to install, becausefrom version v3.52 onwards, it has a hard dependency ongirepository-2.0 (a major upgrade of that library).

This is illustrated by recent build logs from commit7d5d027, both on Ubuntu 22.04 (x86) for Python 3.11, and also on Ubuntu 22.04 (ARM) for Python 3.12:

• https://github.com/matplotlib/matplotlib/actions/runs/14186202430/job/39741858224#step:9:462
• https://github.com/matplotlib/matplotlib/actions/runs/14186202430/job/39741858471#step:9:305

This is related to the changes in#29765; I'd mentioned briefly and obliquely that adding some version pinning might make sense alongside those changes, but hadn't yet suggested it in code:

A compatible possibility would be to place an upper-bound on the version ofPyGObject installed during jobs on previous versions of Ubuntu.

I think that's what we should do (add a version pin - similar to the one in place for MacOS currently - for the Ubuntu 22.04 matrix jobs).

Proposed fix

Use the existingpygobject-ver GitHub Actions CI matrix variable to pin the PythonPyGObject package version to<3.52.0 in Ubuntu 22.04 test workflows, wheregirepository-1.0 is installed.

Edit: add hyperlink topygobject.git v3.52 release notes.