fix(editor): cursor not visible on empty line when line numbers are disabled in code block (#12694)

This fixes an issue where, if line numbers are turned off in a code
block, focusing on an empty line would cause the text cursor to be
hidden.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **Style**
- Updated code block layout to improve appearance when line numbers are
disabled.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: L-Sun <zover.v@gmail.com>

blocksuite/affine/blocks/code/src/styles.ts

@@ -33,6 +33,10 @@ export const codeBlockStyles = css`
     grid-template-columns: auto minmax(0, 1fr);
   }
 
+  .affine-code-block-container.disable-line-numbers v-line {
+    grid-template-columns: unset;
+  }
+
   .affine-code-block-container div:has(> v-line) {
     display: grid;
   }