doc: fix typo in TextEncoding section

PR-URL: #18201
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Khaidi Chu <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Vse Mozhet Byt <[email protected]>
Reviewed-By: Weijia Wang <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>

Author: yosuke-furukawa

doc/api/util.md

@@ -709,7 +709,7 @@ const uint8array = encoder.encode('this is some data');
 UTF-8 encodes the `input` string and returns a `Uint8Array` containing the
 encoded bytes.
 
-### textDecoder.encoding
+### textEncoder.encoding
 
 * {string}