alacritty: Fix deprecation

modules/programs/alacritty/default.nix

@@ -30,6 +30,7 @@ in {
             dynamic_title = true;
             decorations = "full";
             startup_mode = "Windowed";
+            opacity = 0.7;
           };
 
           scrolling = {
@@ -83,7 +84,6 @@ in {
             };
           };
 
-          background_opacity = 0.7;
           mouse_bindings = [ {
             mouse = "Middle";
             action = "PasteSelection";