feat: add commit timestamp to oci-image

flake.nix

@@ -61,6 +61,13 @@
             # See also `rust-toolchain.toml`
             sha256 = "sha256-AJ6LX/Q/Er9kS15bn9iflkUwcgYqRQxiOIL2ToVAXaU=";
           };
+        
+        # The timestamp of the last commit in ISO 8601 format
+        timestamp = pkgs.lib.strings.trim (builtins.readFile (
+          pkgs.runCommand "iso-timestamp" {} ''
+            date -u -d "@${toString inputs.self.lastModified}" +%Y-%m-%dT%H:%M:%SZ > $out
+          ''
+        ));
       });
     in
     inputs.flake-utils.lib.eachDefaultSystem (system:

nix/pkgs/oci-image/default.nix

@@ -3,6 +3,7 @@
 , dockerTools
 , lib
 , pkgs
+, timestamp
 }:
 let
   # See https://github.com/krallin/tini/pull/223
@@ -17,6 +18,7 @@ in
 dockerTools.buildImage {
   name = default.pname;
   tag = "next";
+  created = timestamp;
   copyToRoot = [
     dockerTools.caCertificates
   ];