typo: help format filesize has a wrong example (#16336)

Just a small one letter typo in the help command. It should be `kB`

<img width="943" height="688" alt="image"
src="https://github.com/user-attachments/assets/fcca3978-cc0d-483f-b74e-465743213b76"
/>

crates/nu-command/src/strings/format/filesize.rs

@@ -99,7 +99,7 @@ impl Command for FormatFilesize {
         vec![
             Example {
                 description: "Convert the size column to KB",
-                example: "ls | format filesize KB size",
+                example: "ls | format filesize kB size",
                 result: None,
             },
             Example {