Honor return annotations of async pytest fixtures

Async fixtures skipped the annotation branch, so a `-> T` annotation was
ignored and only the body was inferred. Infer the annotation directly:
the awaited value for coroutines, and the yielded value for annotated
async generators. Add cases where the body is not inferable.

Also drop the tooling note from the AUTHORS entry.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

jedi/plugins/pytest.py

@@ -2,7 +2,9 @@ import sys
 from typing import List
 from pathlib import Path
 
+from jedi.inference.arguments import ValuesArguments
 from jedi.inference.cache import inference_state_method_cache
+from jedi.inference.gradual.annotation import infer_return_types
 from jedi.inference.imports import goto_import, load_module_from_path
 from jedi.inference.filters import ParserTreeFilter
 from jedi.inference.base_value import NO_VALUES, ValueSet
@@ -31,9 +33,20 @@ def execute(callback):
 
 def infer_anonymous_param(func):
     def get_returns(value):
-        # Async fixtures provide the awaited value, rather than a coroutine.
-        if (value.tree_node.annotation is not None
-                and value.tree_node.parent.type != 'async_funcdef'):
+        if value.tree_node.annotation is not None:
+            if value.tree_node.parent.type == 'async_funcdef':
+                # Async fixtures provide the awaited value, rather than a
+                # coroutine. The annotation of an async generator describes
+                # the iterator, so the value is what that iterator yields.
+                result = infer_return_types(value, ValuesArguments([]))
+                if value.as_context().is_generator():
+                    return ValueSet.from_sets(
+                        lazy_value.infer()
+                        for v in result
+                        for lazy_value in v.iterate(is_async=True)
+                    )
+                return result
+
             result = value.execute_with_values()
             if any(v.name.get_qualified_names(include_module_names=True)
                    == ('typing', 'Generator')