Fix the description about the default setting for action in quick start document (#28160)

Since #27054, Actions are enabled by default. so we should also edit the
document. 😃

ps: I think this should be backport to 1.21.0.

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

@@ -23,7 +23,7 @@ First of all, you need a Gitea instance.
 You can follow the [documentation](installation/from-package.md) to set up a new instance or upgrade your existing one.
 It doesn't matter how you install or run Gitea, as long as its version is 1.19.0 or higher.
 
-Actions are disabled by default, so you need to add the following to the configuration file to enable it:
+Since 1.21.0, Actions are enabled by default. If you are using versions before 1.21.0, you need to add the following to the configuration file to enable it:
 
 ```ini
 [actions]

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

@@ -23,7 +23,7 @@ menu:
 您可以按照[文档](installation/from-package.md) 来设置一个新实例或升级现有实例。
 无论您如何安装或运行Gitea，只要版本号是1.19.0或更高即可。
 
-默认情况下，Actions是禁用的，因此您需要将以下内容添加到配置文件中以启用它：
+从1.21.0开始，默认情况下，Actions是启用的。如果您正在使用1.21.0之前的版本，您需要将以下内容添加到配置文件中以启用它：
 
 ```ini
 [actions]