Fix htmlgen html lang (#12668) [backport]

* Fix HTMLGen enable lang on html tag

changelog.md

@@ -53,7 +53,7 @@
 - `htmlgen` adds [MathML](https://wikipedia.org/wiki/MathML) support
   (ISO 40314).
 - `macros.eqIdent` is now invariant to export markers and backtick quotes.
-
+- `htmlgen.html` allows `lang` on the `<html>` tag and common valid attributes.
 
 
 ## Language additions

lib/pure/htmlgen.nim

@@ -321,7 +321,7 @@ macro header*(e: varargs[untyped]): untyped =
 
 macro html*(e: varargs[untyped]): untyped =
   ## generates the HTML ``html`` element.
-  result = xmlCheckedTag(e, "html", "xmlns", "")
+  result = xmlCheckedTag(e, "html", "xmlns" & commonAttr, "")
 
 macro hr*(): untyped =
   ## generates the HTML ``hr`` element.