fix: color style issue of code block in post content snapshot page (#5982)

#### What type of PR is this?

/area ui
/kind bug
/milestone 2.16.x

#### What this PR does / why we need it:

修复在文章版本历史内容预览中代码块颜色显示异常的问题。

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-dev/halo/issues/5845

#### Does this PR introduce a user-facing change?

```release-note
修复在文章版本历史内容预览中代码块颜色显示异常的问题。
```

ui/console-src/modules/contents/posts/components/SnapshotContent.vue

@@ -68,6 +68,7 @@ const { data: snapshot, isLoading } = useQuery({
     margin: 0;
 
     code {
+      color: #ccc;
       background: none;
       font-size: 0.8rem;
       padding: 0 !important;