patch 8.2.3666: libvterm is outdated

Problem:    Libvterm is outdated.
Solution:   Include patches from revision 769 to revision 789.
diff --git a/src/libvterm/t/29state_fallback.test b/src/libvterm/t/29state_fallback.test
index 7995dd1..4ab2e18 100644
--- a/src/libvterm/t/29state_fallback.test
+++ b/src/libvterm/t/29state_fallback.test
@@ -17,3 +17,15 @@
 !Unrecognised DCS
 PUSH "\ePz123\e\\"
   dcs ["z123"]
+
+!Unrecognised APC
+PUSH "\e_z123\e\\"
+  apc ["z123"]
+
+!Unrecognised PM
+PUSH "\e^z123\e\\"
+  pm ["z123"]
+
+!Unrecognised SOS
+PUSH "\eXz123\e\\"
+  sos ["z123"]