While looking over gh-19184, I tried running the test on a machine with sufficient memory on latest main:

python dev.py test -v -j 32 -- -k "test_concatenate_int32_overflow" -rsx

SKIPPED [1] scipy/_lib/tests/test_array_api.py:12: Array API test; set environment variable SCIPY_ARRAY_API=1 to run it

If I remove the slow marker:

--- a/scipy/sparse/tests/test_construct.py
+++ b/scipy/sparse/tests/test_construct.py
@@ -530,7 +530,6 @@ class TestConstructUtils:
         assert isinstance(bmat([[Gm.tocsc(), Gm]], format="csr"), spmatrix)
         assert isinstance(bmat([[Gm, Gm]], format="csc"), spmatrix)
 
-    @pytest.mark.slow
     @pytest.mark.xfail_on_32bit("Can't create large array for test")
     def test_concatenate_int32_overflow(self):
         """ test for indptr overflow when concatenating matrices """

then I can correctly run the test/reproduce the reason for the above PR to exist.

Alternatively, instead of the patch, one can do:

SCIPY_ARRAY_API=1 python dev.py test -m full -v -j 32 -- -k "test_concatenate_int32_overflow", but I don't think that should be needed at this time.

I'm not sure this is particularly serious, at first glance it is just the skip message that is a bit misleading, but would have to think about it more.