[`pyupgrade`] Add fix safety section to `UP004` (#18853)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

Part of #15584

This adds a `Fix safety` section to [useless-object-inheritance
(UP004)](https://docs.astral.sh/ruff/rules/useless-object-inheritance/#useless-object-inheritance-up004)

I could not track down the original PR as this rule is so old it has
gone through several large ruff refactors.
No reasoning is given on the unsafety in the PR/code.
The unsafety is determined here:

f24e650dfd/crates/ruff_linter/src/rules/pyupgrade/rules/useless_class_metaclass_type.rs (L76-L80)

Unsafe fix demonstration:
[playground](https://play.ruff.rs/12b24eb4-d7a5-4ae0-93bb-492d64967ae3)
```py
class A(  # will be deleted
    object
):
    ...
```

## Test Plan

<!-- How was it tested? -->

N/A, no tests/functionality affected

crates/ruff_linter/src/rules/pyupgrade/rules/useless_object_inheritance.rs

@@ -26,6 +26,9 @@ use crate::{AlwaysFixableViolation, Fix};
 /// class Foo: ...
 /// ```
 ///
+/// ## Fix safety
+/// This fix is unsafe if it would cause comments to be deleted.
+///
 /// ## References
 /// - [PEP 3115 – Metaclasses in Python 3000](https://peps.python.org/pep-3115/)
 #[derive(ViolationMetadata)]