Backport build pycapnp 1 for python3.12

[theunkn0wn1]

Please publish pycapnp1.x wheel for manylinux python3.12 .
I have a production application that needs to upgrade to python3.12, but cannot use pycapnp>=2 due to it dropping threading support.
Due to the build requirements for the wheel, pip installs are failing.

[haata]

I currently have no plans to maintain the pycapnp 1.x branch.

If you can submit patches to get the build + CI/CD working, we can figure something out.