Add Closed-Back for april-folls (#3548)

## Description:

Add Closed-Back for april-folls

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:
aotumuri

resources/lang/metadata.json

@@ -23,6 +23,12 @@
     "en": "Catalan",
     "svg": "catalonia"
   },
+  {
+    "code": "cb",
+    "native": "closed bak",
+    "en": "cLoSedBaCk",
+    "svg": "cb_flag"
+  },
   {
     "code": "cs",
     "native": "Čeština",