Fix warnings in CI build pipeline

[sbrugman]

Fix warnings in CI build pipeline:

• [ ] DeprecationWarning: Converting np.inexact or np.floating to a dtype is deprecated. (histogrammar)
• [ ] FutureWarning: In a future version, DataFrame.mean(axis=None) will return a scalar mean over the entire DataFrame.
• [ ] FutureWarning: Dropping of nuisance columns in rolling operations is deprecated; in a future version

We can configure pytest to fail on warnings in pyproject.toml:

filterwarnings = ["error"]

This continues on https://github.com/ing-bank/popmon/pull/262