Crash if using a poor template syntax for tasks arguments

[rik]

In a TOML task definition, forgetting quotes around the name in an argument template will crash mise.

[tasks.foo]
run = ['foo {{arg(name=jobs)}}']

$ mise run foo
The application panicked (crashed).
Message:  called `Result::unwrap()` on an `Err` value: Error { kind: Msg("Failed to render '__tera_one_off'"), source: Some(Error { kind: CallFunction("arg"), source: Some(Error { kind: Msg("Variable `jobs` not found in context while rendering '__tera_one_off'"), source: None }) }) }
Location: src/task/task_script_parser.rs:284

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.

It also crashes when running mise tasks info foo