[flake8-bugbear] Accept immutable slice default arguments (B008) (#21823)

Closes issue #21565

## Summary

As pointed out in the issue, slices are currently flagged by B008 but
this behavior is incorrect because slices are immutable.

## Test Plan

Added a test case in the "B006_B008.py" fixture. Sorry for the diff in
the snapshots, the only thing that changes in those flies is the line
numbers, though.

You can also test this manually with this file:
```py
# test_slice.py
def c(d=slice(0, 3)): ...
```

```sh
> target/debug/ruff check tmp/test_slice.py --no-cache --select B008
All checks passed!
```

crates/ruff_python_stdlib/src/typing.rs

@@ -326,7 +326,15 @@ pub fn is_immutable_return_type(qualified_name: &[&str]) -> bool {
             | ["re", "compile"]
             | [
                 "",
-                "bool" | "bytes" | "complex" | "float" | "frozenset" | "int" | "str" | "tuple"
+                "bool"
+                    | "bytes"
+                    | "complex"
+                    | "float"
+                    | "frozenset"
+                    | "int"
+                    | "str"
+                    | "tuple"
+                    | "slice"
             ]
     )
 }