Ignore DOC errors for stub functions (#12651)

## Summary

Closes https://github.com/astral-sh/ruff/issues/12650.

crates/ruff_linter/resources/test/fixtures/pydoclint/DOC202_google.py

@@ -48,3 +48,14 @@ class Bar:
             num (int): A number
         """
         print('test')
+
+
+# See: https://github.com/astral-sh/ruff/issues/12650
+class C:
+    def foo(self) -> int:
+        """Calculate x.
+
+        Returns:
+            x
+        """
+        raise NotImplementedError

crates/ruff_linter/src/rules/pydoclint/rules/check_docstring.rs

@@ -6,7 +6,8 @@ use ruff_python_ast::helpers::map_callable;
 use ruff_python_ast::name::QualifiedName;
 use ruff_python_ast::visitor::Visitor;
 use ruff_python_ast::{self as ast, visitor, Expr, Stmt};
-use ruff_python_semantic::{Definition, MemberKind, SemanticModel};
+use ruff_python_semantic::analyze::function_type;
+use ruff_python_semantic::{Definition, SemanticModel};
 use ruff_text_size::{Ranged, TextRange};
 
 use crate::checkers::ast::Checker;
@@ -656,15 +657,14 @@ pub(crate) fn check_docstring(
     convention: Option<Convention>,
 ) {
     let mut diagnostics = Vec::new();
-    let Definition::Member(member) = definition else {
+
+    // Only check function docstrings.
+    let Some(function_def) = definition.as_function_def() else {
         return;
     };
 
-    // Only check function docstrings.
+    // Ignore stubs.
-    if matches!(
+    if function_type::is_stub(function_def, checker.semantic()) {
-        member.kind,
-        MemberKind::Class(_) | MemberKind::NestedClass(_)
-    ) {
         return;
     }
 
@@ -681,12 +681,13 @@ pub(crate) fn check_docstring(
 
     let body_entries = {
         let mut visitor = BodyVisitor::new(checker.semantic());
-        visitor.visit_body(member.body());
+        visitor.visit_body(&function_def.body);
         visitor.finish()
     };
 
     // DOC201
-    if checker.enabled(Rule::DocstringMissingReturns) && docstring_sections.returns.is_none() {
+    if checker.enabled(Rule::DocstringMissingReturns) {
+        if docstring_sections.returns.is_none() {
             let extra_property_decorators = checker.settings.pydocstyle.property_decorators();
             if !definition.is_property(extra_property_decorators, checker.semantic()) {
                 if let Some(body_return) = body_entries.returns.first() {
@@ -695,6 +696,7 @@ pub(crate) fn check_docstring(
                 }
             }
         }
+    }
 
     // DOC202
     if checker.enabled(Rule::DocstringExtraneousReturns) {