patch 8.2.1126: Vim9: using :copen causes an error

Problem:    Vim9: using :copen causes an error.
Solution:   Add flag LET_NO_COMMAND in set_var().
diff --git a/src/evalvars.c b/src/evalvars.c
index 1314867..3dab22b 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -2852,7 +2852,7 @@
     typval_T	*tv,
     int		copy)	    // make copy of value in "tv"
 {
-    set_var_const(name, NULL, tv, copy, 0);
+    set_var_const(name, NULL, tv, copy, LET_NO_COMMAND);
 }
 
 /*
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index 8411621..e548717 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -2219,6 +2219,12 @@
   delete('Xvim9_script.vim')
 enddef
 
+def Test_vim9_copen()
+  # this was giving an error for setting w:quickfix_title
+  copen
+  quit
+enddef
+
 " Keep this last, it messes up highlighting.
 def Test_substitute_cmd()
   new
diff --git a/src/version.c b/src/version.c
index b36f248..d1607ae 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1126,
+/**/
     1125,
 /**/
     1124,