doc: fix linter issue

PR-URL: #37657
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

Author: aduh95

doc/api/assert.md

@@ -112,7 +112,7 @@ Legacy assertion mode uses the [Abstract Equality Comparison][] in:
 
 To use legacy assertion mode:
 
-```cjs
+```mjs
 import assert from 'assert';
 ```