Bug#1120569: test-ffc autopkgtest broken by pip 25.3

[Stefano Rivera]

Source: ffc
Version: 2019.2.0~legacy20230509.35df986-5
Severity: serious
Affects: python3-pip

Hi,

debian/tests/test-ffc uses pip to install ffc-factory for the tests. In  
the current version in testing, this shows the fallowing warning:

> Building wheels for collected packages: fenics-ffc-factory
>   DEPRECATION: Building 'fenics-ffc-factory' using the legacy setup.py bdist_wheel mechanism, which will be removed in a future version. pip 25.3 will enforce this behaviour change. A possible replacement is to use the standardized build interface by setting the `--use-pep517` option, (possibly combined with `--no-build-isolation`), or adding a `pyproject.toml` file to the source tree of 'fenics-ffc-factory'. Discussion can be found at https://github.com/pypa/pip/issues/6334

With the latest version of pip in unstable (25.3), this now breaks (as 
promised by the deprecation notice).

Explicitly specifying --use-pep517 should work. You'll need 
--no-build-isolation too, to be able to do this without downloading code 
from the Internet.

Stefano