fix: convert app_id to string before login_as_app_installation call (#340)

Fixes #333

## What

Wrapped `gh_app_id` with `str()` in the `login_as_app_installation` call in
auth.py, and added a targeted test for integer app_id inputs. Existing tests
were also tightened to assert on exact call arguments.

## Why

When `gh_app_id` is passed as an integer, PyJWT raises a TypeError on the
`iss` claim during JWT encoding because it expects a string. This surfaces
at runtime when the environment variable is parsed as an int rather than str.

## Notes

- Only `gh_app_id` is converted; `gh_app_installation_id` is left as-is since `login_as_app_installation` accepts it in its original form — reviewers should verify this is intentional
- The existing tests previously used `assert_called_once()` without argument checks, so bugs like this were invisible; the tightened assertions now catch argument type mismatches

Signed-off-by: jmeridth <jmeridth@gmail.com>

Author: jmeridth

auth.py

@@ -31,7 +31,7 @@ def auth_to_github(
         else:
             gh = github3.github.GitHub()
         gh.login_as_app_installation(
-            gh_app_private_key_bytes, gh_app_id, gh_app_installation_id
+            gh_app_private_key_bytes, str(gh_app_id), gh_app_installation_id
         )
         github_connection = gh
     elif ghe and token:

test_auth.py

@@ -57,7 +57,7 @@ def test_auth_to_github_with_ghe_and_ghe_app(self, mock_ghe):
         result = auth.auth_to_github(
             "", "123", "123", b"123", "https://github.example.com", True
         )
-        mock.login_as_app_installation.assert_called_once()
+        mock.login_as_app_installation.assert_called_once_with(b"123", "123", "123")
         self.assertEqual(result, mock)
 
     @patch("github3.github.GitHub")
@@ -70,7 +70,21 @@ def test_auth_to_github_with_app(self, mock_gh):
         result = auth.auth_to_github(
             "", "123", "123", b"123", "https://github.example.com", False
         )
-        mock.login_as_app_installation.assert_called_once()
+        mock.login_as_app_installation.assert_called_once_with(b"123", "123", "123")
+        self.assertEqual(result, mock)
+
+    @patch("github3.github.GitHub")
+    def test_auth_to_github_with_app_int_app_id(self, mock_gh):
+        """
+        Test that an integer app_id is converted to a string before passing
+        to login_as_app_installation, to avoid PyJWT TypeError on the iss claim.
+        """
+        mock = mock_gh.return_value
+        mock.login_as_app_installation = MagicMock(return_value=True)
+        result = auth.auth_to_github("", 123, 456, b"private_key", "", False)
+        mock.login_as_app_installation.assert_called_once_with(
+            b"private_key", "123", 456
+        )
         self.assertEqual(result, mock)
 
     @patch("github3.login")