Not sure if that is intentional or should rather be considered a bug,
but currently the "structured" option for specifying an external tool
requires that both the command "command" and the "env" keys are
specified. The "command" key makes sense; for the "env" key it came as
a surprise, but it can be argued that this form should only be used when
environment variables need to be specified and the plain string or array
form should be used otherwise.
Either way, the schema did not accurately reflect the current behavior;
now it does. Two sample configs have been added as schema test cases.
While `ui.pager` can be a string which will be tokenized on whitespace,
and argument token array, or a command/env table, the `command` key
within that table currently must be an array. The schema previously
explicitly also allowed it to be a string but that does not actually
work, as exemplified by running:
```sh
$ jj --config-file cli/tests/sample-configs/invalid/ui.pager_command-env_string.toml config list
Config error: Invalid type or value for ui.pager
Caused by: data did not match any variant of untagged enum CommandNameAndArgs
```
`CommandNameAndArgs` should potentially be changed to allow strings.
For now, the schema has been updated to reflect the status quo. A new
sample toml has been added to the `invalid` directory to cover this;
prior to updating the schema, this new test case failed. Once the
behavior is changed to allow string, the file merely needs to be moved
to `valid`.
