fix error msg

[clacrow]

Checklist before merging

• I added an appropriate entry to CHANGELOG.md

The check is OK but the error message is wrong, example:
dataframe.columns = [“A”, “B”]
required_columns = [“B”, “C”]
results in _required_columns={“B”}
and error:
f"Could not find required columns: {“B”} in the table.”
but should be {“C”}

Changed slightly check to fit the error msg.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[lorenzocerrone]

Thanks! Looks good :)