fix(ops/modules/irccat): recursively merge config attribute set

`lib.types.attrs` is deprecated in favor of `lib.types.attrsOf
lib.types.anything` because it doesn't merge attribute sets
/recursively/. `attrsOf` and `anything` do, the former is used to ensure
that the top value is an attribute set as expected by irccat.

Change-Id: I2a9d943a06c8f99f7d6d20c9944288e854924bff
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10129
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

ops/modules/irccat.nix

@@ -33,7 +33,7 @@ in
     enable = lib.mkEnableOption description;
 
     config = lib.mkOption {
-      type = lib.types.attrs; # varying value types
+      type = lib.types.attrsOf lib.types.anything; # varying value types
       description = "Configuration structure (unchecked!)";
     };