Fix typo in find_isomorphisms_between_open_kwarg_dataflow_graphs

[elliottslaughter]

This looks like a typo on find_isomorphisms_between_open_kwarg_dataflow_graphs, or at least it appears to break the pattern of the other bidict passed into the function here (and also just wouldn't seem to make a lot of sense as written).

Passes local tests with the fix.

If I understand the impact it would potentially create false negatives (i.e., missing legitimate errors) but cannot create false positives (making working code look like it fails). So I guess it's good that the test suite passes, which would seem to indicate we haven't missed anything because of this.

However, there is likely inadequate test coverage because we missed this, and I haven't made any attempt so far to chase down what test case would be required to actually exercise the fix.

---

This change is 

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (5f49bc7) to head (c9d0a99).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@      Coverage Diff       @@
##   master   #1638   +/-   ##
==============================
==============================

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.