patch 8.2.1477: Vim9: error when using bufnr('%')

Problem:    Vim9: error when using bufnr('%').
Solution:   Don't give an error for using a string argument. (closes #6723)

src/evalbuffer.c

@@ -390,6 +390,7 @@ f_bufnr(typval_T *argvars, typval_T *rettv)
 	buf = curbuf;
     else
     {
+	if (argvars[0].v_type != VAR_STRING)
 	    (void)tv_get_number(&argvars[0]);    // issue errmsg if type error
 	++emsg_off;
 	buf = tv_get_buf(&argvars[0], FALSE);

src/testdir/test_vim9_func.vim

@@ -1315,6 +1315,11 @@ def Test_filter_return_type()
   assert_equal(6, res)
 enddef
 
+def Test_bufnr()
+  let buf = bufnr()
+  assert_equal(buf, bufnr('%'))
+enddef
+
 def Test_getreg_return_type()
   let s1: string = getreg('"')
   let s2: string = getreg('"', 1)

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1477,
 /**/
     1476,
 /**/