Fix type of commit for create_file

The `commit` key of `create_file`'s result currently uses
`github.Commit.Commit`, but that does not match the data model of the
endpoint: while ill documented on docs.github.com, looking at the
published schema (via https://github.com/github/rest-api-description
or more readably https://github.com/octokit/types.ts which is
automatically generated from the former) `file-commit.commit` looks
significantly more like a `git-commit` than a `commit`:

* `commit`'s author and committer are git*hub* objects
  (`nullable-simple-user`), while `file-commit.commit`'s are git
  objects (triplets of name, email, and date)
* `commit` embeds the tree, and message in a sub-object, while
  `file-commit.commit` has them at the toplevel
* `file-commit.commit` has no `stats` or `files` properties, or
  `comments_url`

In all of these, `file-commit.commit` matches `git-commit` exactly.

The only real divergence between `git-commit` and `file-commit.commit`
is that the schema indicates all of `file-commit.commit`'s properties
are optional, but I think it's a case of the endpoint being
under-specified and the properties *not* being marked required, rather
than them being explicitly optional. See
github/rest-api-description#650 for an issue
on that subject with more information.

github/Repository.py

@@ -2188,7 +2188,7 @@ def create_file(
         :param author: InputGitAuthor, (optional), if omitted this will be filled in with committer information. If passed, you must specify both a name and email.
         :rtype: {
             'content': :class:`ContentFile <github.ContentFile.ContentFile>`:,
-            'commit': :class:`Commit <github.Commit.Commit>`}
+            'commit': :class:`Commit <github.GitCommit.GitCommit>`}
         """
         assert isinstance(path, str)
         assert isinstance(message, str)
@@ -2223,7 +2223,7 @@ def create_file(
             "content": github.ContentFile.ContentFile(
                 self._requester, headers, data["content"], completed=False
             ),
-            "commit": github.Commit.Commit(
+            "commit": github.GitCommit.GitCommit(
                 self._requester, headers, data["commit"], completed=True
             ),
         }

github/Repository.pyi

@@ -142,7 +142,7 @@ class Repository(CompletableGithubObject):
         branch: Union[str, _NotSetType] = ...,
         committer: Union[InputGitAuthor, _NotSetType] = ...,
         author: Union[InputGitAuthor, _NotSetType] = ...,
-    ) -> Dict[str, Union[ContentFile, Commit]]: ...
+    ) -> Dict[str, Union[ContentFile, GitCommit]]: ...
     def create_git_blob(self, content: str, encoding: str) -> GitBlob: ...
     def create_git_commit(
         self,

tests/Repository.py

@@ -1412,14 +1412,37 @@ def testCreateFile(self):
             "Enix Yu", "enix223@163.com", "2016-01-15T16:13:30+12:00"
         )
         self.assertEqual(repr(author), 'InputGitAuthor(name="Enix Yu")')
-        self.repo.create_file(
+        result = self.repo.create_file(
             path=newFile,
             message="Create file for testCreateFile",
             content=content,
             branch="master",
             committer=author,
             author=author,
         )
+        commit = result["commit"]
+        raw_keys = set(commit.raw_data.keys())
+        self.assertLessEqual(
+            {
+                "sha",
+                "parents",
+                "tree",
+                "author",
+                "committer",
+                "url",
+                "html_url",
+                # missing from replay data but documented in schema
+                # "node_id",
+                # "message",
+                # "verification",
+            },
+            raw_keys,
+            "raw data should match (be a subset of) git-commit keys",
+        )
+        self.assertFalse(
+            {"comments_url", "commit", "stats", "files"} & raw_keys,
+            "characteristic attributes of commit should not be in the raw data",
+        )
 
     def testUpdateFile(self):
         updateFile = "doc/testCreateUpdateDeleteFile.md"