missing_symbol -> missing_value_symbol (#1902)

Author: Bahex

blog/2025-04-29-nushell_0_104_0.md

@@ -174,7 +174,7 @@ ps | where name == bash | kill ...$in.pid
 Missing values (not `null`) are represented by ❎ in tables. [#15647](https://github.com/nushell/nushell/pull/15647) from [@Bahex](https://github.com/Bahex) makes this indicator configurable. For example:
 
 ```nushell
-$env.config.table.missing_symbol = " ∅ "
+$env.config.table.missing_value_symbol = " ∅ "
 ```
 
 ### Some `math` commands now work with bounded ranges [[toc](#table-of-contents)]