At present, `ISC001` and `ISC002` flag concatenations like the following:
```py
"a" "b" # ISC001
"a" \
"b" # ISC002
```
However, multiline concatenations are allowed.
This PR adds a setting:
```toml
[tool.ruff.flake8-implicit-str-concat]
allow-multiline = false
```
Which extends `ISC002` to _also_ flag multiline concatenations, like:
```py
(
"a" # ISC002
"b"
)
```
Note that this is backwards compatible, as `allow-multiline` defaults to `true`.
cc63a4be6a