stylix: downgrade and lock tinted-kitty input (danth#589)

Downgrade and lock the tinted-kitty input to avoid upstream breaking
changes.

Considering that Stylix eventually re-implements tinted-kitty's
functionality [1], it might be easiest to lock this input to avoid
wasted maintenance effort.

This downgrade revokes commit 5699ba9 ("stylix: bump tinted-kitty
input (danth#588)"), which resolved the issue "bug: inconsistent color
between terminals (foot & kitty)" [2] by pulling [3]. Since the desired
commit [3] follows the commit introducing the breaking changes [4], it
cannot be pulled without resolving these breaking changes.

[1]: danth#534
[2]: danth#567
[3]: tinted-theming/tinted-kitty@292c717
[4]: tinted-theming/tinted-kitty@9569d8a

Link: danth#571
Link: danth#589

flake.nix

@@ -59,7 +59,15 @@
 
     tinted-kitty = {
       flake = false;
-      url = "github:tinted-theming/tinted-kitty";
+
+      # Lock the tinted-kitty input to prevent upstream breaking changes.
+      #
+      # Considering that Stylix eventually re-implements this input's
+      # functionality [1], it might be easiest to lock this input to avoid
+      # wasted maintenance effort.
+      #
+      # [1]: https://github.com/danth/stylix/issues/534
+      url = "github:tinted-theming/tinted-kitty/eb39e141db14baef052893285df9f266df041ff8";
     };
   };