Do not add an extra blank line to an import line that has fmt disabled

[yilei]

Description

Fixes #3438.

This isn't put in preview style because:

1. Already formatted code always has the extra blank line, so it shouldn't change already formatted code and doesn't violate the stability policy.
2. This unblocks us from upstreaming the incremental formatting patches in Pyink, and we don't want to require --preview (in at least in 2023) to use this feature. It would also make integrations with IDEs / pre-commit harder if we require --preview.

Checklist - did you ...

• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

[github-actions]

diff-shades reports zero changes comparing this PR (c7fa452) to main (fc6cea0).

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