fix: mark int64 as either number or BigInt (#489)

Part of octokit/request.js#797

Author: wolfy1339

packages/openapi-types-ghec/types.d.ts

@@ -97,6 +97,11 @@ type Repository = components["schemas"]["full-repository"]
             ? "string | File | Uint8Array | Blob | null"
             : "string | File | Uint8Array | Blob";
         }
+        if (schemaObject.format === "int64") {
+          return schemaObject.nullable
+            ? "number | bigint | null"
+            : "number | bigint";
+        }
         return undefined;
       },
     });