fix: reflect renames of Nix configuration options

Change-Id: I7e28ac3d71acd7d99a1d3ef97bef9422097e4abf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6154
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

ops/modules/tvl-cache.nix

@@ -6,12 +6,12 @@
   };
 
   config = lib.mkIf config.tvl.cache.enable {
-    nix = {
-      binaryCachePublicKeys = [
+    nix.settings = {
+      trusted-public-keys = [
         "cache.tvl.su:kjc6KOMupXc1vHVufJUoDUYeLzbwSr9abcAKdn/U1Jk="
       ];
 
-      binaryCaches = [
+      substituters = [
         "https://cache.tvl.su"
       ];
     };