docs: add missing comma to seo plugin doc (#11516)

Add missing comma

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Author: yagee

docs/plugins/seo.mdx

@@ -293,7 +293,7 @@ All types can be directly imported:
 import type {
   PluginConfig,
   GenerateTitle,
-  GenerateDescription
+  GenerateDescription,
   GenerateURL
 } from '@payloadcms/plugin-seo/types';
 ```