### 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)

("--show-dagrun",),
    help=(
        "After completing the backfill, shows the diagram for current DAG Run.\n"
        "\n"
        "The diagram is in DOT language\n"
    ),
    action="store_true",
)
ARG_IMGCAT_DAGRUN = Arg(
    ("--imgcat-dagrun",),
    help=(
        "After completing the dag run, prints a diagram on the screen for the "
        "current DAG Run using the imgcat tool.\n"
    ),
    action="store_true",
)
ARG_SAVE_DAGRUN = Arg(
    ("--save-dagrun",),
    help="After completing the backfill, saves the diagram for current DAG Run to the indicated file.\n\n",
)
ARG_TREE = Arg(("-t", "--tree"), help="Tree view", action="store_true")
ARG_SHUT_DOWN_LOGGING = Arg(
    ("--no-shut-down-logging",),
    help=argparse.SUPPRESS,
    dest="shut_down_logging",
    action="store_false",
    default=True,
)
ARG_UPSTREAM = Arg(("-u", "--upstream"), help="Include upstream tasks", action="store_true")
ARG_ONLY_FAILED = Arg(("-f", "--only-failed"), help="Only failed jobs", action="store_true")