Allow to set GitHub API version

This adds a new set_api_version method the GitHub class that accepts
an API version string as defined in [1].  The version is added to the
session headers.  Sessions headers remain unchanged if no version string
was given.

Addresses #1121.

[1]: https://docs.github.com/en/rest/overview/api-versions?apiVersion=2022-11-28

Author: anz-ableton

src/github3/github.py

@@ -2596,6 +2596,17 @@ def set_client_id(self, id, secret):
         """
         self.session.params = {"client_id": id, "client_secret": secret}
 
+    def set_api_version(self, api_version):
+        """Allow to set a specific API version.
+
+        :param str api_version:
+            API version to send with X-GitHub-Api-Version header.
+            See https://docs.github.com/en/rest/overview/api-versions?apiVersion=2022-11-28 for details on API versions.
+        """  # noqa: E501
+        if not api_version:
+            return
+        self.session.headers.update({"X-GitHub-Api-Version": api_version})
+
     def set_user_agent(self, user_agent):
         """Allow the user to set their own user agent string.
 

tests/unit/test_github.py

@@ -727,6 +727,12 @@ def test_set_user_agent_required_user_agent(self):
 
         self.session.headers.update.called is False
 
+    def test_set_api_version(self):
+        self.instance.set_api_version("2022-11-28")
+        self.session.headers.update.assert_called_once_with(
+            {"X-GitHub-Api-Version": "2022-11-28"}
+        )
+
     def test_set_user_agent(self):
         self.instance.set_user_agent("github3py")
         self.session.headers.update.assert_called_once_with(