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

@@ -16,7 +16,7 @@
 
 def get_jwt(github_id: str | None = None, github_private_key: str | None = None) -> str:
     if github_id is None:
-        github_id = options.get("github-app.id")
+        github_id = str(options.get("github-app.id"))
     if github_private_key is None:
         github_private_key = options.get("github-app.private-key")
     exp_ = datetime.datetime.utcnow() + datetime.timedelta(minutes=10)

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")