Update flake.lock, bump helium, and fix SSH config

Refresh locked revisions in flake.lock to newer commits, update the
helium
AppImage to version 0.12.4.1, and replace the SSH module's matchBlocks
attribute with the new settings attribute.

modules/home/ssh.nix

@@ -2,7 +2,7 @@
   programs.ssh = {
     enable = true;
     enableDefaultConfig = false;
-    matchBlocks = {
+    settings = {
       "hp-t640-homeserver" = {
         hostname = "192.168.1.156";
         user = "${username}";