Merge branch 'bugfix-single-obs-key' of https://github.com/zincware/Z…

…nH5MD into bugfix-single-obs-key

tests/test_single_obs_key.py

@@ -41,4 +41,4 @@ def test_single_entry_calc(tmp_path):
     io.extend([water for _ in range(5)])
     assert len(io) == 6
     assert len(io[:]) == 6
-    assert len(list(io)) == 6
+    assert len(list(io)) == 6