treewide: set shebang for bash scripts

These scripts previously failed when called with syscalls like
`execve` (used by, e.g., Python's `subprocess.run`) that use no default
interpreter for scripts without a shebang.

modules/lnd.nix

@@ -109,7 +109,7 @@ let
       description = "The package providing lnd binaries.";
     };
     cli = mkOption {
-      default = pkgs.writeScriptBin "lncli"
+      default = pkgs.writers.writeBashBin "lncli"
         # Switch user because lnd makes datadir contents readable by user only
         ''
           ${runAsUser} ${cfg.user} ${cfg.package}/bin/lncli \