Fix 2.4 migration examples

doc/manual/src/release-notes/rl-2.4.md

@@ -281,7 +281,9 @@ more than 2800 commits from 195 contributors since release 2.3.
 * The `nix` command is now marked as an experimental feature. This
   means that you need to add
 
-  > experimental-features = nix-command
+  ```
+  experimental-features = nix-command
+  ```
 
   to your `nix.conf` if you want to use it, or pass
   `--extra-experimental-features nix-command` on the command line.
@@ -289,30 +291,42 @@ more than 2800 commits from 195 contributors since release 2.3.
 * The `nix` command no longer has a syntax for referring to packages
   in a channel. This means that the following no longer works:
 
-  > nix build nixpkgs.hello # Nix 2.3
+  ```console
+  nix build nixpkgs.hello # Nix 2.3
+  ```
 
   Instead, you can either use the `#` syntax to select a package from
   a flake, e.g.
 
-  > nix build nixpkgs#hello
+  ```console
+  nix build nixpkgs#hello
+  ```
 
   Or, if you want to use the `nixpkgs` channel in the `NIX_PATH`
   environment variable:
 
-  > nix build -f '<nixpkgs>' hello
+  ```console
+  nix build -f '<nixpkgs>' hello
+  ```
 
 * The old `nix run` has been renamed to `nix shell`, while there is a
   new `nix run` that runs a default command. So instead of
 
-  > nix run nixpkgs.hello -c hello # Nix 2.3
+  ```console
+  nix run nixpkgs.hello -c hello # Nix 2.3
+  ```
 
   you should use
 
-  > nix shell nixpkgs#hello -c hello
+  ```console
+  nix shell nixpkgs#hello -c hello
+  ```
 
   or just
 
-  > nix run nixpkgs#hello
+  ```console
+  nix run nixpkgs#hello
+  ```
 
   if the command you want to run has the same name as the package.