Replace <iframe> → <fencedframe> in the Accessibility section (#3…

…7454)

The documentation of `<fencedframe>` contains leftovers copied from the documentation of `<iframe>` in its *Accessibility* section, which makes it confusing to read.

files/en-us/web/html/element/fencedframe/index.md

@@ -78,7 +78,7 @@ People navigating with assistive technology such as a screen reader can use the
   height="320"></fencedframe>
 ```
 
-Without this title, they have to navigate into the `<iframe>` to determine what its embedded content is. This context shift can be confusing and time-consuming, especially for pages with multiple `<iframe>`s and/or if embeds contain interactive content like video or audio.
+Without this title, they have to navigate into the `<fencedframe>` to determine what its embedded content is. This context shift can be confusing and time-consuming, especially for pages with multiple `<fencedframe>`s and/or if embeds contain interactive content like video or audio.
 
 ## Examples