patch 8.2.3631: "syntax enable" does not work properly in Vim9 context

Problem:    "syntax enable" does not work properly in Vim9 context.
Solution:   Also handle Vim9 context. (closes #9161)
diff --git a/src/syntax.c b/src/syntax.c
index b3545b3..3002bc9 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -3777,7 +3777,7 @@
     static void
 syn_cmd_enable(exarg_T *eap, int syncing UNUSED)
 {
-    set_internal_string_var((char_u *)"syntax_cmd", (char_u *)"enable");
+    set_internal_string_var((char_u *)"g:syntax_cmd", (char_u *)"enable");
     syn_cmd_onoff(eap, "syntax");
     do_unlet((char_u *)"g:syntax_cmd", TRUE);
 }
@@ -3792,7 +3792,7 @@
     set_nextcmd(eap, eap->arg);
     if (!eap->skip)
     {
-	set_internal_string_var((char_u *)"syntax_cmd", (char_u *)"reset");
+	set_internal_string_var((char_u *)"g:syntax_cmd", (char_u *)"reset");
 	do_cmdline_cmd((char_u *)"runtime! syntax/syncolor.vim");
 	do_unlet((char_u *)"g:syntax_cmd", TRUE);
     }
diff --git a/src/testdir/test_vim9_cmd.vim b/src/testdir/test_vim9_cmd.vim
index ee381ed..0fa65d1 100644
--- a/src/testdir/test_vim9_cmd.vim
+++ b/src/testdir/test_vim9_cmd.vim
@@ -1581,5 +1581,13 @@
   set previewpopup&
 enddef
 
+def Test_syntax_enable_clear()
+  syntax clear
+  syntax enable
+  highlight clear String
+  assert_equal(true, hlget('String')->get(0, {})->get('default', false))
+  syntax clear
+enddef
+
 
 " vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker
diff --git a/src/version.c b/src/version.c
index 4fb0e9e..79eb94f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3631,
+/**/
     3630,
 /**/
     3629,