fix(language): fix khmer language rendering by adding missing 'ligatures' property (@Earpengai) (monkeytypegame#6132)

### Description

Minor update ligatures to Khmer language.

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---------

Co-authored-by: Ear Pengai <[email protected]>

Author: Earpengai

frontend/static/languages/khmer.json

@@ -1,5 +1,6 @@
 {
   "name": "khmer",
+  "ligatures": true,
   "noLazyMode": true,
   "bcp47": "km-KH",
   "words": [