doc: fix typo in webstreams.md

`deccompressionStream.writable` -> `decompressionStream.writable`.

PR-URL: #39898
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

Author: lpinca

doc/api/webstreams.md

@@ -1263,7 +1263,7 @@ added: v16.7.0
 
 * Type: {ReadableStream}
 
-#### `deccompressionStream.writable`
+#### `decompressionStream.writable`
 <!-- YAML
 added: v16.7.0
 -->