requests: Annotate Session.merge_environment_settings (#8313)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

stubs/requests/requests/sessions.pyi

@@ -1,7 +1,7 @@
 from _typeshed import Self, SupportsItems, SupportsRead
 from collections.abc import Callable, Iterable, Mapping, MutableMapping
 from typing import IO, Any, Union
-from typing_extensions import TypeAlias
+from typing_extensions import TypeAlias, TypedDict
 
 from urllib3._collections import RecentlyUsedContainer
 
@@ -75,6 +75,12 @@ _HeadersUpdateMapping: TypeAlias = Mapping[str, str | bytes | None]
 _Timeout: TypeAlias = Union[float, tuple[float, float], tuple[float, None]]
 _Verify: TypeAlias = bool | str
 
+class _Settings(TypedDict):
+    verify: _Verify | None
+    proxies: _TextMapping
+    stream: bool
+    cert: _Cert | None
+
 class Session(SessionRedirectMixin):
     __attrs__: Any
     headers: CaseInsensitiveDict[str | bytes]
@@ -86,8 +92,8 @@ class Session(SessionRedirectMixin):
     hooks: dict[str, list[_Hook] | Any]
     params: _Params
     stream: bool
-    verify: None | bool | str
-    cert: None | str | tuple[str, str]
+    verify: _Verify | None
+    cert: _Cert | None
     max_redirects: int
     trust_env: bool
     cookies: RequestsCookieJar
@@ -261,7 +267,14 @@ class Session(SessionRedirectMixin):
         allow_redirects: bool = ...,
         **kwargs: Any,
     ) -> Response: ...
-    def merge_environment_settings(self, url, proxies, stream, verify, cert): ...
+    def merge_environment_settings(
+        self,
+        url: str | bytes | None,
+        proxies: _TextMapping | None,
+        stream: bool | None,
+        verify: _Verify | None,
+        cert: _Cert | None,
+    ) -> _Settings: ...
     def get_adapter(self, url: str) -> _BaseAdapter: ...
     def close(self) -> None: ...
     def mount(self, prefix: str | bytes, adapter: _BaseAdapter) -> None: ...