see https://ci.debian.net/data/autopkgtest/testing/i386/s/sagemath/36323965/log.gz

[...]
7183s Total time for all tests: 6888.5 seconds
7183s     cpu time: 10109.5 seconds
7183s     cumulative wall time: 13105.7 seconds
7183s Features detected for doctesting:
sage.combinat,sage.geometry.polyhedron,sage.graphs,sage.plot,sage.rings.number_field,sage.rings.real_double,sage.symbolic,sagemath_doc_html,sphinx
7183s Pytest is not installed, skip checking tests that rely on it.
7183s Success: 186 tests failed, up to 200 failures are tolerated
7183s Error: critical test failures (e.g. timeout, segfault, etc.)
7183s make: *** [debian/tests.mk:57: had-few-failures] Error 1

I think this is fixed upstream. Apparently they were made aware that this particular failing test just takes a long time, but if you give it a couple minutes it does pass.