requests: Add regression test for #8762 (#8835)

The final mypy_primer report for #8762 was an empty diff. Considering the number of issues we've had with our requests stubs over the last year, it feels like it makes sense to add a test case to make sure that it doesn't regress.

stubs/requests/@tests/test_cases/check_post.py

@@ -1,13 +1,58 @@
 # pyright: reportUnnecessaryTypeIgnoreComment=true
 
+from __future__ import annotations
+
+from collections.abc import Iterable
+
 import requests
 
+# =================================================================================================
 # Regression test for #7988 (multiple files should be allowed for the "files" argument)
-# This snippet comes from the requests documentation (https://requests.readthedocs.io/en/latest/user/advanced/#post-multiple-multipart-encoded-files),
+# This snippet comes from the requests documentation
+# (https://requests.readthedocs.io/en/latest/user/advanced/#post-multiple-multipart-encoded-files),
 # so should pass a type checker without error
+# =================================================================================================
+
+
 url = "https://httpbin.org/post"
 multiple_files = [
     ("images", ("foo.png", open("foo.png", "rb"), "image/png")),
     ("images", ("bar.png", open("bar.png", "rb"), "image/png")),
 ]
 r = requests.post(url, files=multiple_files)
+
+
+# =================================================================================
+# Tests for various different types being passed into the "data" parameter
+# (These all return "Any", so there's not much value in using assert_type here.)
+# (Just test that type checkers don't emit an error if it doesn't fail at runtime.)
+# =================================================================================
+
+
+# Arbitrary iterable
+def gen() -> Iterable[bytes]:
+    yield b"foo"
+    yield b"bar"
+
+
+requests.post("http://httpbin.org/anything", data=gen()).json()["data"]
+
+# bytes
+requests.post("http://httpbin.org/anything", data=b"foobar").json()["data"]
+
+# str
+requests.post("http://httpbin.org/anything", data="foobar").json()["data"]
+
+# Files
+requests.post("http://httpbin.org/anything", data=open("/tmp/foobar", "rb")).json()["data"]
+requests.post("http://httpbin.org/anything", data=open("/tmp/foobar", "r")).json()["data"]
+
+# Mappings
+requests.post("http://httpbin.org/anything", data={b"foo": b"bar"}).json()["form"]
+requests.post("http://httpbin.org/anything", data={"foo": "bar"}).json()["form"]
+
+# mappings represented by an list/tuple of key-values pairs
+requests.post("http://httpbin.org/anything", data=[(b"foo", b"bar")]).json()["form"]
+requests.post("http://httpbin.org/anything", data=[("foo", "bar")]).json()["form"]
+requests.post("http://httpbin.org/anything", data=((b"foo", b"bar"),)).json()["form"]
+requests.post("http://httpbin.org/anything", data=(("foo", "bar"),)).json()["form"]