fix: update email icon in mkdocs configuration

mkdocs.yml

@@ -65,7 +65,7 @@ extra:
       link: https://mineru.space/common/qun/?qid=362634
       name: WeChat
     - icon: material/email
-      link: OpenDataLab@pjlab.org.cn
+      link: mailto:OpenDataLab@pjlab.org.cn
       name: E-mail
 
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