Restrict PYI034 for in-place operations to enclosing class (#24511)

## Summary

In `.py` and `.pyi` files, we now only flag cases in which the return
type is the enclosing class, like:

```python
class A:
    def __iadd__(self) -> A:
        return self
```

As opposed to:

```python
class A:
    def __iadd__(self) -> int:
        return self
```

Closes https://github.com/astral-sh/ruff/issues/24462.

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI034.py

@@ -392,3 +392,8 @@ class UsesStringizedForwardReferences:
     def __enter__(self) -> "UsesStringizedForwardReferences": ...    # PYI034
     async def __aenter__(self) -> "UsesStringizedForwardReferences": ...  # PYI034
     def __iadd__(self, other) -> "UsesStringizedForwardReferences": ...  # PYI034
+
+
+class InPlaceOperationReturningOtherTypeAtRuntime:
+    def __iadd__(self, other: int) -> int:
+        return 1

crates/ruff_linter/resources/test/fixtures/flake8_pyi/PYI034.pyi

@@ -277,3 +277,7 @@ class MetaclassInWhichSelfCannotBeUsed7(django.db.models.base.ModelBase):
 class MetaclassInWhichSelfCannotBeUsed8(django.db.models.base.ModelBase):
     def __new__(cls, name: builtins.str, bases: tuple, attributes: dict, /, **kw) -> MetaclassInWhichSelfCannotBeUsed8:
         ...
+
+
+class StubInPlaceOperationReturningOtherType:
+    def __iadd__(self, other: int) -> int: ...

crates/ruff_linter/src/rules/flake8_pyi/rules/non_self_return_type.rs

@@ -42,7 +42,8 @@ use ruff_text_size::Ranged;
 /// Specifically, this check enforces that the return type of the following
 /// methods is `Self`:
 ///
-/// 1. In-place binary-operation dunder methods, like `__iadd__`, `__imul__`, etc.
+/// 1. In-place binary-operation dunder methods, like `__iadd__`, `__imul__`, etc.,
+///    if those methods return the class name.
 /// 1. `__new__`, `__enter__`, and `__aenter__`, if those methods return the
 ///    class name.
 /// 1. `__iter__` methods that return `Iterator`, despite the class inheriting
@@ -192,7 +193,7 @@ pub(crate) fn non_self_return_type(
 
     // In-place methods that are expected to return `Self`.
     if is_inplace_bin_op(name) {
-        if !is_self(returns, checker) {
+        if is_name_or_stringized_name(returns, &class_def.name, checker) {
             add_diagnostic(checker, stmt, returns, class_def, name);
         }
         return;
@@ -330,13 +331,6 @@ fn is_name_or_stringized_name(expr: &ast::Expr, name: &str, checker: &Checker) -
     checker.match_maybe_stringized_annotation(expr, |expr| is_name(expr, name))
 }
 
-/// Return `true` if the given expression resolves to `typing.Self`.
-fn is_self(expr: &ast::Expr, checker: &Checker) -> bool {
-    checker.match_maybe_stringized_annotation(expr, |expr| {
-        checker.semantic().match_typing_expr(expr, "Self")
-    })
-}
-
 /// Return `true` if the given class extends `collections.abc.Iterator`.
 fn subclasses_iterator(class_def: &ast::StmtClassDef, semantic: &SemanticModel) -> bool {
     analyze::class::any_qualified_base_class(class_def, semantic, |qualified_name| {

crates/ruff_linter/src/rules/flake8_pyi/snapshots/ruff_linter__rules__flake8_pyi__tests__PYI034_PYI034.py.snap

@@ -511,6 +511,7 @@ help: Use `Self` as return type
 392 +     def __enter__(self) -> typing.Self: ...    # PYI034
 393 |     async def __aenter__(self) -> "UsesStringizedForwardReferences": ...  # PYI034
 394 |     def __iadd__(self, other) -> "UsesStringizedForwardReferences": ...  # PYI034
+395 |
 note: This is an unsafe fix and may change runtime behavior
 
 PYI034 [*] `__aenter__` methods in classes like `UsesStringizedForwardReferences` usually return `self` at runtime
@@ -529,6 +530,8 @@ help: Use `Self` as return type
     -     async def __aenter__(self) -> "UsesStringizedForwardReferences": ...  # PYI034
 393 +     async def __aenter__(self) -> typing.Self: ...  # PYI034
 394 |     def __iadd__(self, other) -> "UsesStringizedForwardReferences": ...  # PYI034
+395 |
+396 |
 note: This is an unsafe fix and may change runtime behavior
 
 PYI034 [*] `__iadd__` methods in classes like `UsesStringizedForwardReferences` usually return `self` at runtime
@@ -545,4 +548,7 @@ help: Use `Self` as return type
 393 |     async def __aenter__(self) -> "UsesStringizedForwardReferences": ...  # PYI034
     -     def __iadd__(self, other) -> "UsesStringizedForwardReferences": ...  # PYI034
 394 +     def __iadd__(self, other) -> typing.Self: ...  # PYI034
+395 |
+396 |
+397 | class InPlaceOperationReturningOtherTypeAtRuntime:
 note: This is an unsafe fix and may change runtime behavior