ci: add patched nextcloud-talk-desktop to binary cache

Includes the Wayland screen sharing patch (from ash/talk-desktop-wayland-screenshare)
and adds custom-nextcloud-talk-desktop to CI build-and-cache pipeline.

.gitea/workflows/ci.yml

@@ -51,6 +51,7 @@ jobs:
             custom-beads
             custom-gastown
             custom-perles
+            custom-nextcloud-talk-desktop
             qt-pinned-jellyfin-media-player
             qt-pinned-stremio
             nix-deck-kernel

flake.nix

@@ -285,6 +285,7 @@
         "custom-mcrcon-rbw" = pkgs.custom.mcrcon-rbw;
         "custom-tea-rbw" = pkgs.custom.tea-rbw;
         "custom-rclone-torbox-setup" = pkgs.custom.rclone-torbox-setup;
+        "custom-nextcloud-talk-desktop" = pkgs.custom.nextcloud-talk-desktop;
         "qt-pinned-jellyfin-media-player" = pkgsQt.jellyfin-media-player;
         "qt-pinned-stremio" = pkgsQt.stremio;
         # Flake input packages (beads, gastown) - these get version from input rev