fix: do not print usage on runtime error (#1315)

## Description
---
> Should include a concise description of the changes (bug or feature),
it's
> impact, along with a summary of the solution

## PR Checklist
---
> Thank you for opening a Pull Request! Before submitting your PR, there
are a
> few things you can do to make sure it goes smoothly:
- [ ] Make sure you reviewed

[CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
- [ ] Make sure to open an issue as a

[bug/issue](https://github.com/googleapis/langchain-google-alloydb-pg-python/issues/new/choose)
before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)
- [ ] Make sure to add `!` if this involve a breaking change

🛠️ Fixes #<issue_number_goes_here>

cmd/root.go

@@ -219,6 +219,9 @@ func NewCommand(opts ...Option) *Command {
 		o(cmd)
 	}
 
+	// Do not print Usage on runtime error
+	cmd.SilenceUsage = true
+
 	// Set server version
 	cmd.cfg.Version = versionString