fix: narrow exception handling in get_github_app_installation_token

## What/Why
Narrow except clause from bare Exception to GithubException so that
misconfiguration errors (bad int() cast, JWT construction failures)
propagate instead of silently returning None and causing confusing 401s
downstream. Addresses PR review feedback from @zkoppert.

## Proof it works
All 14 tests in test_auth.py pass. Updated the request_failure test to
raise GithubException instead of bare Exception to match the narrowed
catch. Pylint clean (no new warnings).

## Risk + AI role
Low. AI-generated (Claude Opus 4.6) with human review.

## Review focus
Whether GithubException covers all the API/network error cases we want
to catch, or if additional specific exceptions should be included.

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

Author: jmeridth

auth.py

@@ -1,7 +1,7 @@
 """This is the module that contains functions related to authenticating to GitHub with a personal access token."""
 
 import env
-from github import Auth, Github, GithubIntegration
+from github import Auth, Github, GithubException, GithubIntegration
 
 
 def auth_to_github(
@@ -81,6 +81,6 @@ def get_github_app_installation_token(
             gi = GithubIntegration(auth=app_auth)
         installation_token = gi.get_access_token(int(gh_app_installation_id))
         return installation_token.token
-    except Exception as e:  # pylint: disable=broad-exception-caught
+    except GithubException as e:
         print(f"Request failed: {e}")
         return None

test_auth.py

@@ -4,6 +4,7 @@
 from unittest.mock import MagicMock, patch
 
 import auth
+from github import GithubException
 
 
 class TestAuth(unittest.TestCase):
@@ -262,7 +263,9 @@ def test_get_github_app_installation_token_request_failure(
         mock_app_auth_cls.return_value = mock_app_auth
         mock_gi = MagicMock()
         mock_gi_cls.return_value = mock_gi
-        mock_gi.get_access_token.side_effect = Exception("Request failed")
+        mock_gi.get_access_token.side_effect = GithubException(
+            500, "Request failed", None
+        )
 
         result = auth.get_github_app_installation_token(
             ghe="https://api.github.com",