Syntax highlighting broken for code blocks created with triple backticks

[ysds]

Describe the bug
When inserting a code block using triple backticks (```), syntax highlighting doesn't work based on the defaultLanguage setting.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://www.blocknotejs.org/examples/theming/code-block
2. Type ``` to create a code block
3. Enter const x = 3 * 4;
4. Syntax highlighting doesn't work (even though JavaScript is selected in the dropdown)
5. Select a different language, and syntax highlighting starts working

Expected behavior

• Syntax highlighting should work based on the defaultLanguage setting

However, it works correctly when inserting code blocks through the Suggestion Menu or when pasting markdown that contains code blocks with language specification.

Misc

• Node version:
• Package manager:
• Browser: Chrome 140.0.7339.133
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