devenv: apply mdbook 0.5 support patch to devenv_nix

Apply the mdbook 0.5 support patch to devenv's bundled Nix 2.30.4.

The patch is from upstream Nix commit 5cbd7856, which maintains
compatibility with both mdbook 0.4.x and 0.5.x. The doc/manual/package.nix
file is excluded as it doesn't exist in cachix's Nix fork.

https://github.com/NixOS/nix/issues/14628

pkgs/by-name/de/devenv/package.nix

@@ -1,6 +1,7 @@
 {
   lib,
   fetchFromGitHub,
+  fetchpatch2,
   gitMinimal,
   makeBinaryWrapper,
   installShellFiles,
@@ -20,16 +21,27 @@ let
   devenvNixVersion = "2.30.4";
 
   devenv_nix =
+    let
+      components =
+        (nixVersions.nixComponents_git.override { version = devenvNixVersion; }).overrideSource
+          (fetchFromGitHub {
+            owner = "cachix";
+            repo = "nix";
+            rev = "devenv-${devenvNixVersion}";
+            hash = "sha256-3+GHIYGg4U9XKUN4rg473frIVNn8YD06bjwxKS1IPrU=";
+          });
+    in
     (
-      (nixVersions.nixComponents_git.override { version = devenvNixVersion; })
-      .nix-everything.overrideSource
-      (fetchFromGitHub {
-        owner = "cachix";
-        repo = "nix";
-        rev = "devenv-${devenvNixVersion}";
-        hash = "sha256-3+GHIYGg4U9XKUN4rg473frIVNn8YD06bjwxKS1IPrU=";
-      })
-    ).overrideAttrs
+      # Support for mdbook >= 0.5, https://github.com/NixOS/nix/issues/14628
+      components.appendPatches [
+        (fetchpatch2 {
+          name = "nix-2.30-14695-mdbook-0.5-support.patch";
+          url = "https://github.com/NixOS/nix/commit/5cbd7856de0a9c13351f98e32a1e26d0854d87fd.patch";
+          excludes = [ "doc/manual/package.nix" ];
+          hash = "sha256-GYaTOG9wZT9UI4G6za535PkLyjHKSxwBjJsXbjmI26g=";
+        })
+      ]
+    ).nix-everything.overrideAttrs
       (old: {
         pname = "devenv-nix";
         version = devenvNixVersion;