fix(github): Cast app ID to string for PyJWT 2.12.0 iss claim

PyJWT 2.11.0+ validates that the iss claim must be a string during
encoding. The github-app.id and github.integration-app-id options are
registered with default=0 (int), so options.get() returns an int,
causing InvalidClaimError. Cast to str() in both JWT generation paths.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: michelletran-sentry

src/sentry/integrations/github/utils.py

@@ -28,7 +28,7 @@ def get_jwt(github_id: str | None = None, github_private_key: str | None = None)
         # JWT expiration time (10 minute maximum)
         "exp": exp,
         # Integration's GitHub identifier
-        "iss": github_id,
+        "iss": str(github_id),
     }
     return jwt.encode(payload, github_private_key, algorithm="RS256")
 

src/sentry_plugins/github/client.py

@@ -99,7 +99,7 @@ def get_jwt(self) -> str:
             # JWT expiration time (10 minute maximum)
             "exp": exp,
             # Integration's GitHub identifier
-            "iss": options.get("github.integration-app-id"),
+            "iss": str(options.get("github.integration-app-id")),
         }
 
         return jwt.encode(payload, options.get("github.integration-private-key"), algorithm="RS256")