feat(language): add bosnian 4k (@aitchz) (#6432)

### Description

add bosnian_4k

### Checks

- [x] Adding a language or a theme?
- [x] If is a language, did you edit `_list.json`, `_groups.json` and
add `languages.json`?
- [x] Check if any open issues are related to this PR; if so, be sure to
tag them below.
- [x] Make sure the PR title follows the Conventional Commits standard.
(https://www.conventionalcommits.org for more info)
- [x] Make sure to include your GitHub username prefixed with @ inside
parentheses at the end of the PR title.

---------

Co-authored-by: Miodec <jack@monkeytype.com>

frontend/static/languages/_groups.json

@@ -377,7 +377,7 @@
   },
   {
     "name": "bosnian",
-    "languages": ["bosnian"]
+    "languages": ["bosnian", "bosnian_4k"]
   },
   {
     "name": "esperanto",

frontend/static/languages/_list.json

@@ -228,6 +228,7 @@
   ,"bangla_letters"
   ,"bangla_10k"
   ,"bosnian"
+  ,"bosnian_4k"
   ,"toki_pona"
   ,"toki_pona_ku_suli"
   ,"toki_pona_ku_lili"
@@ -397,4 +398,4 @@
   ,"code_common_lisp"
   ,"docker_file"
   ,"code_fortran"
-]
+]