AssertionError in test_whichdb_ndbm on NetBSD

[furkanonder]

Bug report

Bug description:

home$ ./python -m test test_dbm -m test_whichdb_ndbm
Using random seed: 1067465967
0:00:00 load avg: 0.00 Run 1 test sequentially in a single process
0:00:00 load avg: 0.00 [1/1] test_dbm
test test_dbm failed -- Traceback (most recent call last):
  File "/home/blue/cpython/Lib/test/test_dbm.py", line 221, in test_whichdb_ndbm
    self.assertIsNone(self.dbm.whichdb(path))
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 'dbm.ndbm' is not None

test_dbm failed (1 failure)

== Tests result: FAILURE ==

1 test failed:
    test_dbm

Total duration: 285 ms
Total tests: run=1 (filtered) failures=1
Total test files: run=1/1 (filtered) failed=1
Result: FAILURE

OS: NetBSD 10.0 amd64

CPython versions tested on:

CPython main branch

Operating systems tested on:

Other

[furkanonder]

CC: @serhiy-storchaka