patch 8.2.1616: Vim9: cannot pass "true" to synID()

Problem:    Vim9: cannot pass "true" to synID().
Solution:   Use tv_get_bool_chk(). (closes #6860)

src/evalfunc.c

@@ -8487,7 +8487,7 @@ f_synID(typval_T *argvars UNUSED, typval_T *rettv)
 
     lnum = tv_get_lnum(argvars);		// -1 on type error
     col = (linenr_T)tv_get_number(&argvars[1]) - 1;	// -1 on type error
-    trans = (int)tv_get_number_chk(&argvars[2], &transerr);
+    trans = (int)tv_get_bool_chk(&argvars[2], &transerr);
 
     if (!transerr && lnum >= 1 && lnum <= curbuf->b_ml.ml_line_count
 	    && col >= 0 && col < (long)STRLEN(ml_get(lnum)))

src/testdir/test_vim9_func.vim

@@ -1551,6 +1551,13 @@ def Test_searchdecl()
   assert_equal(1, searchdecl('blah', true, true))
 enddef
 
+def Test_synID()
+  new
+  setline(1, "text")
+  assert_equal(0, synID(1, 1, true))
+  bwipe!
+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 */
+/**/
+    1616,
 /**/
     1615,
 /**/