### Description

Currently, the `airflow variables export` command requires an explicit file path and does not support output to stdout. However connections can be printed to stdout using `airflow connections export -`. This inconsistency between the two export commands can lead to confusion and limits the flexibility of the variables export command.

### Use case/motivation

To bring some consistency, similar to connections, variables should also be printed to STDOUT, using `-` instead of filename. 

### Related issues

_No response_

### Are you willing to submit a PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

ARG_DAG_ID,
            ARG_TASK_REGEX,
            ARG_START_DATE,
            ARG_END_DATE,
            ARG_MARK_SUCCESS,
            ARG_LOCAL,
            ARG_DONOT_PICKLE,
            ARG_YES,
            ARG_CONTINUE_ON_FAILURES,
            ARG_DISABLE_RETRY,
            ARG_BF_IGNORE_DEPENDENCIES,
            ARG_BF_IGNORE_FIRST_DEPENDS_ON_PAST,
            ARG_SUBDIR,
            ARG_POOL,
            ARG_DELAY_ON_LIMIT,
            ARG_DRY_RUN,
            ARG_VERBOSE,
            ARG_CONF,
            ARG_RESET_DAG_RUN,
            ARG_RERUN_FAILED_TASKS,
            ARG_RUN_BACKWARDS,
            ARG_TREAT_DAG_AS_REGEX,
        ),
    ),
    ActionCommand(
        name="test",
        help="Execute one single DagRun",
        description=(
            "Execute one single DagRun for a given DAG and execution date.\n"
            "\n"