Fix error message in ScalarInequality

[amontanez24]

Environment Details

Please indicate the following details about the environment in which you found the bug:

• SDV version: 0.16.0.dev0
• Python version: Any
• Operating System: Any

Error Description

If I pass in an invalid value as the "value" parameter, the error says:
ValueError: `value` must be a number or datetime.

This is not technically correct. The value should be a string that represents a datetime.
New Error should say:
Value Error: `value` must be a number or a string that represents a datetime.

Steps to reproduce

constraint = ScalarInequality(column_name='age', relation='>=', value=False)