Avoid leading newline with float-to-top

[sakshichitnis27]

Fixes #1935

Summary

• Avoid applying lines_before_imports during the preliminary float_to_top pass.
• Let the normal sorting pass apply the configured spacing in the correct location.
• Add a regression test ensuring module docstrings remain at the beginning of the file.

Testing

• Reproduced the original issue using lines_before_imports = 1 and float_to_top = true.
• Verified that the module docstring remains on the first line after the fix.
• pytest -q — 621 passed, 2 skipped
• pytest -q tests/unit/test_regressions.py -k "float_to_top or lines_before_imports"
• ruff check isort/core.py tests/unit/test_regressions.py
• mypy isort/core.py tests/unit/test_regressions.py
• flake8 isort/core.py tests/unit/test_regressions.py
• isort --check-only isort/core.py tests/unit/test_regressions.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.39%. Comparing base (a8c0004) to head (d955593).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2583   +/-   ##
=======================================
  Coverage   99.39%   99.39%           
=======================================
  Files          41       41           
  Lines        3137     3137           
  Branches      680      680           
=======================================
  Hits         3118     3118           
  Misses         11       11           
  Partials        8        8           

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[DanielNoord]

Thanks for the fix!

It works, but I don't think this is how we'd like to solve this. I'd expect the fix to actually be in sorted_imports instead of overwriting a configuration value on the fly. That could have unintended side effects. Do you think you can fix this without doing this?