Fix highlighting of module parameter

Disallow nested ocamlModParam. For some reason the ocamlModParam was
opened twice, but closed only once.

Co-authored-by: Samuel Hym <[email protected]>

Author: n-osborne

syntax/ocaml.vim

@@ -142,7 +142,7 @@ syn match    ocamlKeyword "\<include\>" skipwhite skipempty nextgroup=ocamlModPa
 " 2022-10: please document it?
 syn region   ocamlModule matchgroup=ocamlKeyword start="\<module\>" matchgroup=ocamlModule end="\<_\|\u\(\w\|'\)*\>" contains=@ocamlAllErrs,@ocamlCommentLike skipwhite skipempty nextgroup=ocamlPreDef
 syn region   ocamlPreDef start="."me=e-1 end="[a-z:=)]\@=" contained contains=@ocamlAllErrs,@ocamlCommentLike,ocamlModParam,ocamlGenMod,ocamlModTypeRestr nextgroup=ocamlModTypePre,ocamlModPreRHS
-syn region   ocamlModParam start="(\*\@!" end=")" contained contains=ocamlGenMod,ocamlModParam,ocamlModParam1,ocamlSig,ocamlVal
+syn region   ocamlModParam start="(\*\@!" end=")" contained contains=ocamlGenMod,ocamlModParam1,ocamlSig,ocamlVal
 syn match    ocamlModParam1 "\<\u\(\w\|'\)*\>" contained skipwhite skipempty
 syn match    ocamlGenMod "()" contained skipwhite skipempty