k9s: fix broken completion scripts on aarch64-darwin

k9s apparently requires a writeable log location. Before this commit;
the generated bash, fish, and zsh completion files in the
aarch64-darwin* build had as their first line the error message:
Fail to init k9s logs location could not create any of the following paths: /homeless-shelter/Library/Application Support

* Yes, really only on  aarch64-darwin. x86_64-darwin, x86_64-linux, and
  aarch64-linux are fine. Don't ask me why.

pkgs/applications/networking/cluster/k9s/default.nix

@@ -42,6 +42,11 @@ buildGoModule rec {
 
   nativeBuildInputs = [ installShellFiles ];
   postInstall = ''
+    # k9s requires a writeable log directory
+    # Otherwise an error message is printed
+    # into the completion scripts
+    export K9S_LOGS_DIR=$(mktemp -d)
+
     installShellCompletion --cmd k9s \
       --bash <($out/bin/k9s completion bash) \
       --fish <($out/bin/k9s completion fish) \