[pyflakes] Fix false positive for names shadowing re-exports (F811) (#23356)

## Summary

Fixes #10874.

In stub files, explicit re-exports (`from x import y as y`) at module
scope were falsely flagged as redefined (F811) by class-scoped
attributes with the same name. A class attribute binding in a nested
scope should not invalidate a module-level re-export.

Skip the F811 diagnostic when the shadowed binding is an explicit
re-export (`is_explicit_export()`).

## Test plan

- Reproduction case: `ruff check --select F811 stub.pyi` no longer emits
false positive
- `cargo test -p ruff_linter -- pyflakes` — all 462 tests pass

Author: kar-ganap

crates/ruff_linter/resources/test/fixtures/pyflakes/F811_33.pyi

@@ -0,0 +1,7 @@
+# Regression test for https://github.com/astral-sh/ruff/issues/10874
+# Explicit re-exports at module scope should not be flagged as redefined
+# by class-scoped attributes with the same name.
+from x import y as y
+
+class Foo:
+    y = 42  # OK — class attribute, different scope from module-level re-export

crates/ruff_linter/src/rules/pyflakes/mod.rs

@@ -132,6 +132,7 @@ mod tests {
     #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_30.py"))]
     #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_31.py"))]
     #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_32.py"))]
+    #[test_case(Rule::RedefinedWhileUnused, Path::new("F811_33.pyi"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_0.py"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_1.py"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_2.py"))]

crates/ruff_linter/src/rules/pyflakes/rules/redefined_while_unused.rs

@@ -126,6 +126,13 @@ pub(crate) fn redefined_while_unused(checker: &Checker, scope_id: ScopeId, scope
                 ) {
                     continue;
                 }
+
+                // Don't flag explicit re-exports (e.g., `from x import y as y`).
+                // A binding in a nested scope (like a class attribute) doesn't
+                // invalidate a module-level re-export.
+                if shadowed.is_explicit_export() {
+                    continue;
+                }
             }
 
             // If the bindings are in different forks, abort.

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F811_F811_33.pyi.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+