lisa.tests.starting.utilclamp: Fix for pandas 2.0.0
DataFrame.pivot(index=None) seems to have changed behavior: https://github.com/pandas-dev/pandas/issues/52436
Remove index=None so that it works across pandas versions.
DataFrame.pivot(index=None) seems to have changed behavior: https://github.com/pandas-dev/pandas/issues/52436
Remove index=None so that it works across pandas versions.