patch 8.2.2584: Vim9: type error for assigning "any" to a list

Problem:    Vim9: type error for assigning the result of list concatenation to
            a list.
Solution:   Do not consider concatenation result in a constant. (closes #7942)

src/testdir/test_vim9_expr.vim

@@ -1370,6 +1370,9 @@ def Test_expr5_list_add()
     dany[i] = i
   endfor
   assert_equal({a: 'a', 12: 12}, dany)
+
+  # result of glob() is "any", runtime type check
+  var sl: list<string> = glob('*.txt', false, true) + ['']
 enddef
 
 " test multiply, divide, modulo

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2584,
 /**/
     2583,
 /**/

src/vim9compile.c

@@ -4450,7 +4450,7 @@ compile_expr6(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 }
 
 /*
- *      +	number addition
+ *      +	number addition or list/blobl concatenation
  *      -	number subtraction
  *      ..	string concatenation
  */
@@ -4532,6 +4532,7 @@ compile_expr5(char_u **arg, cctx_T *cctx, ppconst_T *ppconst)
 	else
 	{
 	    generate_ppconst(cctx, ppconst);
+	    ppconst->pp_is_const = FALSE;
 	    if (*op == '.')
 	    {
 		if (may_generate_2STRING(-2, cctx) == FAIL