fluxcd: build with CGO_ENABLED=0 to match upstream

The upstream Makefile and goreleaser config both build with
CGO_ENABLED=0. This produces a fully static binary and ensures
consistent behavior (e.g., pure-Go DNS resolver) across all
platforms.

pkgs/by-name/fl/fluxcd/package.nix

@@ -39,6 +39,8 @@ buildGoModule rec {
     rm source/cmd/flux/create_secret_git_test.go
   '';
 
+  env.CGO_ENABLED = 0;
+
   ldflags = [
     "-s"
     "-w"