Update Actions documentation missing feature (#31034)

Fix
https://github.com/go-gitea/gitea/issues/25897#issuecomment-2117145391

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: yp05327 <576951401@qq.com>

docs/content/usage/actions/comparison.en-us.md

@@ -108,6 +108,10 @@ See [Creating an annotation for an error](https://docs.github.com/en/actions/usi
 
 It's ignored by Gitea Actions now.
 
+### Expressions
+
+For [expressions](https://docs.github.com/en/actions/learn-github-actions/expressions), only [`always()`](https://docs.github.com/en/actions/learn-github-actions/expressions#always) is supported.
+
 ## Missing UI features
 
 ### Pre and Post steps

docs/content/usage/actions/comparison.zh-cn.md

@@ -108,6 +108,10 @@ Gitea Actions目前不支持此功能。
 
 Gitea Actions目前不支持此功能。
 
+### 表达式
+
+对于 [表达式](https://docs.github.com/en/actions/learn-github-actions/expressions), 当前仅 [`always()`](https://docs.github.com/en/actions/learn-github-actions/expressions#always) 被支持。
+
 ## 缺失的UI功能
 
 ### 预处理和后处理步骤