linbox `master`: `test-cra` fails on `ubuntu-xenial-toolchain-gcc_9`, `debian-bullseye-standard`

[mkoeppe]

On ubuntu-xenial-toolchain-gcc_9-minimal), tested using

• ci-sage: Update fflas-ffpack#386

 [linbox-git]   FAIL: test-cra

https://github.com/linbox-team/fflas-ffpack/actions/runs/7382353719/job/20082049565?pr=386#step:11:2442

Likewise on debian-bullseye-standard, see https://github.com/linbox-team/fflas-ffpack/actions/runs/7382353719/job/20082050525?pr=386#step:14:4769