Make ruff format idempotent when using stdin input

[leiserfg]

Summary

Currently, this happens

$ echo "print()" | ruff format - 

#Notice that nothing went to stdout

Which does not match ruff check --fix - behavior and deletes my code every time I format it (more or less 5 times per minute 😄).

I just checked that my example works as the change was very straightforward.

[codspeed-hq]

CodSpeed Performance Report

Merging #7581 will improve performances by 2.33%

_{Comparing leiserfg:fix-format-stdin (839a55f) with main (c3774e1)}

Summary

⚡ 1 improvements
✅ 24 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	leiserfg:fix-format-stdin	Change
⚡	linter/all-rules[numpy/ctypeslib.py]	35 ms	34.2 ms	+2.33%

[github-actions]

PR Check Results

Ecosystem

✅ ecosystem check detected no changes.

[charliermarsh]

Thank you! This makes sense.