patch 8.2.1606: Vim9: cannot use "true" with has()

Problem:    Vim9: cannot use "true" with has().
Solution:   Use tv_get_bool(). (closes #6876)

src/evalfunc.c

@@ -4763,7 +4763,7 @@ f_has(typval_T *argvars, typval_T *rettv)
 	}
     }
 
-    if (argvars[1].v_type != VAR_UNKNOWN && tv_get_number(&argvars[1]) != 0)
+    if (argvars[1].v_type != VAR_UNKNOWN && tv_get_bool(&argvars[1]))
 	// return whether feature could ever be enabled
 	rettv->vval.v_number = x;
     else

src/testdir/test_vim9_func.vim

@@ -1516,6 +1516,10 @@ def Test_getcompletion()
   set wildignore&
 enddef
 
+def Test_has()
+  assert_equal(1, has('eval', true))
+enddef
+
 def Fibonacci(n: number): number
   if n < 2
     return n

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1606,
 /**/
     1605,
 /**/