Fix line number settings migration (#41351)

Follow-up to https://github.com/zed-industries/zed/pull/39268

Also updates the documentation.

Release Notes:

- N/A

crates/migrator/src/migrations/m_2025_10_21/settings.rs

@@ -9,6 +9,7 @@ pub fn make_relative_line_numbers_an_enum(value: &mut Value) -> Result<()> {
     *relative_line_numbers = match relative_line_numbers {
         Value::Bool(true) => Value::String("enabled".to_string()),
         Value::Bool(false) => Value::String("disabled".to_string()),
+        Value::String(s) if s == "enabled" || s == "disabled" || s == "wrapped" => return Ok(()),
         _ => anyhow::bail!("Expected relative_line_numbers to be a boolean"),
     };
     Ok(())