fix: handle multiline string in parameter formatting

[finswimmer]

This PR fixes an issue where multiline string parameters in function were formatted by docformatter.

If the input looked like this:

foo = textwrap.dedent("""\
   bar
   baz
""")

The wrong output looked like this:

foo = textwrap.dedent(\
"""\
   bar
   baz
"""\
)

My expectation is that docformatter do nothing in this case.

I was able to narrow down the underlying issue by myself. The actual fix was than created with the help of AI, as my knowledge about the token stuff is quite limited 🙈