Refseq can have several entries with same strain. Take into account in tests

test/test_unit/test_prepare/test_download.py

@@ -318,7 +318,7 @@ def test_download_specify_strains(caplog):
     # Check path to uncompressed files is as expected
     assert db_dir == os.path.join(outdir, "Database_init")
     # Check number of genomes downloaded
-    assert nb_gen == 4
+    assert nb_gen >= 4 # there can be several genomes with same strain and spe_taxid (1 complete and one contigs for example)
     # And that db_dir exists and contains nb_gen files
     assert os.path.isdir(db_dir)
     assert len(os.listdir(db_dir)) == nb_gen