[MC-262714] The "key.keyboard.unknown" string displayed within the key binds menu is improperly capitalized

The Bug:

The "key.keyboard.unknown" string displayed within the key binds menu is improperly capitalized.

Every other piece of text within the key binds menu has all its words capitalized, for example, "Middle Button", "Left Button", "Right Button", and "Keypad Decimal" but "Not bound" doesn't, therefore introducing an inconsistency. This could be intentional, but I'm reporting it just in case.

Affected String:

Before reading the table, please note the following:

Words colored in GREEN are correct.
Words colored in RED are incorrect.

Translation Key	Current String	Expected String	String URL on Crowdin
key.keyboard.caps.lock	Caps Lock	Caps Lock	https://crowdin.com/translate/minecraft/10038/enus-engb#5333274
key.keyboard.keypad.enter	Keypad Enter	Keypad Enter	https://crowdin.com/translate/minecraft/10038/enus-engb#5333256
key.keyboard.down	Down Arrow	Down Arrow	https://crowdin.com/translate/minecraft/10038/enus-engb#5333312
key.keyboard.left.control	Left Control	Left Control	https://crowdin.com/translate/minecraft/10038/enus-engb#5333286
key.keyboard.num.lock	Num Lock	Num Lock	https://crowdin.com/translate/minecraft/10038/enus-engb#5333272
key.keyboard.page.down	Page Down	Page Down	https://crowdin.com/translate/minecraft/10038/enus-engb#5333278
key.keyboard.unknown	Not bound	Not Bound	https://crowdin.com/translate/minecraft/10038/enus-engb#5333156

Steps to Reproduce:

Display the affected string by using the command provided below.
```
/tellraw @s {"translate":"key.keyboard.unknown"}
```
Look closely at the affected word within the string.
Take note as to whether or not the "key.keyboard.unknown" string displayed within the key binds menu is improperly capitalized.

Observed Behavior:

The string is improperly capitalized.

Expected Behavior:

The string would be properly capitalized.