nixos/image: fix layout of option examples in repart builder

nixos/modules/image/repart.nix

···
           };
         });
         default = { };
-        example = lib.literalExpression '' {
-          "/EFI/BOOT/BOOTX64.EFI".source =
-            "''${pkgs.systemd}/lib/systemd/boot/efi/systemd-bootx64.efi";
+        example = lib.literalExpression ''
+          {
+            "/EFI/BOOT/BOOTX64.EFI".source =
+              "''${pkgs.systemd}/lib/systemd/boot/efi/systemd-bootx64.efi";
 
-          "/loader/entries/nixos.conf".source = systemdBootEntry;
-        }
+            "/loader/entries/nixos.conf".source = systemdBootEntry;
+          }
         '';
         description = lib.mdDoc "The contents to end up in the filesystem image.";
       };
···
     partitions = lib.mkOption {
       type = with lib.types; attrsOf (submodule partitionOptions);
       default = { };
-      example = lib.literalExpression '' {
-        "10-esp" = {
-          contents = {
-            "/EFI/BOOT/BOOTX64.EFI".source =
-              "''${pkgs.systemd}/lib/systemd/boot/efi/systemd-bootx64.efi";
-          }
-          repartConfig = {
-            Type = "esp";
-            Format = "fat";
+      example = lib.literalExpression ''
+        {
+          "10-esp" = {
+            contents = {
+              "/EFI/BOOT/BOOTX64.EFI".source =
+                "''${pkgs.systemd}/lib/systemd/boot/efi/systemd-bootx64.efi";
+            }
+            repartConfig = {
+              Type = "esp";
+              Format = "fat";
+            };
           };
-        };
-        "20-root" = {
-          storePaths = [ config.system.build.toplevel ];
-          repartConfig = {
-            Type = "root";
-            Format = "ext4";
-            Minimize = "guess";
+          "20-root" = {
+            storePaths = [ config.system.build.toplevel ];
+            repartConfig = {
+              Type = "root";
+              Format = "ext4";
+              Minimize = "guess";
+            };
           };
         };
-      };
       '';
       description = lib.mdDoc ''
         Specify partitions as a set of the names of the partitions with their