devenv: fix version mismatch (2.0.7 reported instead of 2.0.6)

Upstream tagged v2.0.6 with the workspace Cargo.toml already bumped to
2.0.7, causing the binary to report the wrong version. This also breaks
devenv.lock version checks for users.

Fixes https://github.com/cachix/devenv/issues/2682

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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

@@ -53,6 +53,11 @@ rustPlatform.buildRustPackage {
 
   cargoHash = "sha256-p5kI7HlG6RVxCCEb/J0L2gh36jkm/atAV98ny3h4vqo=";
 
+  # Upstream tagged v2.0.6 with Cargo.toml already bumped to 2.0.7
+  postPatch = ''
+    substituteInPlace Cargo.toml --replace-fail 'version = "2.0.7"' 'version = "${version}"'
+  '';
+
   env = {
     RUSTFLAGS = "--cfg tracing_unstable";
     LIBSQLITE3_SYS_USE_PKG_CONFIG = "1";