Use double quote instead of backtick to clarify Ellipsis constant (GH-9754)

Doc/library/constants.rst

@@ -53,8 +53,8 @@ A small number of constants live in the built-in namespace.  They are:
 
 .. data:: Ellipsis
 
-   The same as ``...``.  Special value used mostly in conjunction with extended
-   slicing syntax for user-defined container data types.
+   The same as the ellipsis literal "...".  Special value used mostly in conjunction
+   with extended slicing syntax for user-defined container data types.
 
 
 .. data:: __debug__
@@ -96,4 +96,3 @@ should not be used in programs.
    Object that when printed, prints the message "Type license() to see the
    full license text", and when called, displays the full license text in a
    pager-like fashion (one screen at a time).
-