Preview does not show Syntax Highlighting

**Describe the bug**
The preview does not show syntax highlighting. This is probably a minor bug at best.

**To Reproduce**
Steps to reproduce the behavior:

1. Start writing a new issue
2. Write the following (do not copy, there are zero width spaces between the backticks):
```
Here is a bug.
`​`​`java
public static void main(String[] testCode) {
assert(false);
}
`​`​`
```
3. Click "Preview"
4. No syntax highlighting.

**Expected behavior**
Syntax highlighting for Java code.

**Screenshots**

**Desktop (please complete the following information):**

- OS: Windows 10
- Browser: Chrome
- Browser Version: Version 106.0.5249.103 (Official Build) (64-bit)

Reproduce the issue in a new issue by entering the provided Java fenced code block and selecting Preview. Trace the TypeScript issue-editor preview and its Markdown or syntax-highlighting entry point; no file or test is named in the report. Done means Java code blocks visibly receive syntax highlighting in Preview without breaking other preview behavior.

Written by the indexing model from the issue text.