Update rule B005 docs (#8028)

## Summary

Rule B005 of flake8-bugbear docs has a typo in one of the examples that
leads to a confusion in the correctness of `.strip()` method


![image](https://github.com/astral-sh/ruff/assets/104530599/b4e19751-558e-4ebb-b82f-25c321ddc32b)

```python
# Wrong output (used in docs) 
"text.txt".strip(".txt")  # "ex" 

# Correct output
"text.txt".strip(".txt")  # "e"
```

crates/ruff_linter/src/rules/flake8_bugbear/rules/strip_with_multi_characters.rs

@@ -34,7 +34,7 @@ use crate::checkers::ast::Checker;
 ///
 /// ## Example
 /// ```python
-/// "text.txt".strip(".txt")  # "ex"
+/// "text.txt".strip(".txt")  # "e"
 /// ```
 ///
 /// Use instead: