EM101: Exception must not use a string literal, assign to variable first

This seems a simple enough to auto-fix given the example

current

    raise XYZ(<some-kind-of-string>)

autofix to:

    msg = <some-kind-of-string>
    raise XYZ(msg)

1. if msg has been previously defined, we could still fail (with an unfixable message) (or try weird names for the variable like message, xyz_msg, xyz_message, error_msg, error_message, etc.)

Verified no autofix for:

• ruff: ruff 0.1.7
• python: 3.11
• nothing relevant to em101 in pyproject.toml (except selecting "EM")