gopls: fix build in darwin sandbox

The versionCheckHook clears the environment, so gopls fails to create
its cache directory as it defaults to a read-only dir. Pass TMPDIR to
fix.

See https://github.com/NixOS/nixpkgs/issues/473777

pkgs/by-name/go/gopls/package.nix

@@ -36,6 +36,7 @@ buildGoLatestModule (finalAttrs: {
 
   doInstallCheck = true;
   nativeInstallCheckInputs = [ versionCheckHook ];
+  versionCheckKeepEnvironment = [ "TMPDIR" ];
   versionCheckProgramArg = "version";
 
   passthru.updateScript = nix-update-script { extraArgs = [ "--version-regex=gopls/(.*)" ]; };