fix: style issue of the fullscreen button in Code input (#6785)

#### What type of PR is this?

/area ui
/kind bug
/milestone 2.20.x

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

为 Code Input 设置默认高度，修复全屏按钮被遮挡的问题。

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

Fixes https://github.com/halo-dev/halo/issues/6681

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

```release-note
为 Code Input 设置默认高度，修复全屏按钮被遮挡的问题。
```

ui/src/formkit/inputs/code/CodeInput.vue

@@ -39,7 +39,7 @@ useEventListener(codeInputWrapperRef, "keydown", (e: KeyboardEvent) => {
       ref="codeInputWrapperRef"
       :style="{ height }"
       :class="{ '!fixed inset-0 z-[999] !block bg-white': fullscreen }"
-      class="group relative w-full"
+      class="group relative h-9 w-full"
     >
       <VPageHeader v-if="fullscreen" :title="context.label" class="border-b">
         <template #actions>