W291: ruff --fix removes trailing whitespace in multiline string

[Jasha10]

When W291 (trailing-whitespace) is enabled, ruff warns about trailing whitespace in multiline strings.
When --fix is passed, ruff modifies the multiline string. This could result in a behavior change of the python code.

Repro:

# repro.py
string = """
this line has trailing whitespace 
"""

$ ruff repro.py --isolated --select W291
repro.py:3:34: W291 [*] Trailing whitespace
Found 1 error.
[*] 1 potentially fixable with the --fix option.
$ ruff repro.py --isolated --select W291 --fix  # This modifies the multiline string!
Found 1 error (1 fixed, 0 remaining).
$ ruff --version
ruff 0.0.278

I noticed that the implementation trailing_whitespace categorizes the --fix action as Fix::safe_edit. I feel that modifying a multiline string is not safe; it can change the behavior of my python code. The doc for Applicability::Safe say:

    /// The fix is safe and can always be applied.
    /// The fix is definitely what the user intended, or it maintains the exact meaning of the code.

I feel that this does not apply to W291 as implemented.

[charliermarsh]

Yeah, we should change to unsafe_edit when the diagnostic is inside a multiline string.