[lex.key,diff.header.iso646.h] Consistent tokens order (#3190)

Order the alternative tokens in [diff.header.iso646.h] in the same way
they are ordered in Table 6 in [lex.key].

Author: danra

source/compatibility.tex

@@ -2462,8 +2462,8 @@
 \tcode{bitand},
 \tcode{bitor},
 \tcode{compl},
-\tcode{not_eq},
 \tcode{not},
+\tcode{not_eq},
 \tcode{or},
 \tcode{or_eq},
 \tcode{xor},