Helm 4 compatibility

When using the plugin with Helm 4, I have the following error:

```console
Error: Failed to render chart: exit status 1: Flag --validate has been deprecated, use '--dry-run=server' instead
Error: if any flags in the group [validate dry-run] are set none of the others can be; [dry-run validate] were all set

Error: plugin "diff" exited with error
```