perf(github): Cache only required fields for accessible repos

Strip raw GitHub repo dicts down to the 5 fields used by
get_repositories before storing in the cache. Reduces per-integration
cache size from ~3KB per repo to ~100 bytes.

Author: jaydgoss

src/sentry/integrations/github/client.py

@@ -550,18 +550,25 @@ def get_repos(self, page_number_limit: int | None = None) -> list[dict[str, Any]
                 page_number_limit=page_number_limit,
             )
 
+    # Fields from the GitHub API response needed by get_repositories().
+    _CACHED_REPO_FIELDS = ("id", "name", "full_name", "default_branch", "archived")
+
     def get_accessible_repos_cached(self, ttl: int = 300) -> list[dict[str, Any]]:
         """
         Return all repos accessible to this installation.
         Cached in Django cache for ``ttl`` seconds so that debounced
         search keystrokes don't re-fetch all pages from GitHub.
+
+        Only the fields used by get_repositories() are stored to keep
+        the cache payload small.
         """
         cache_key = f"github:accessible_repos:{self.integration.id}"
         cached = default_cache.get(cache_key)
         if cached is not None:
             return cached
 
-        repos = self.get_repos()
+        all_repos = self.get_repos()
+        repos = [{k: r.get(k) for k in self._CACHED_REPO_FIELDS} for r in all_repos]
         default_cache.set(cache_key, repos, ttl)
         return repos