Fix corrupted output for backslash-continued imports with trailing semicolons

[Copilot]

When a backslash-continued import had a semicolon in the continuation line, isort would corrupt the output by treating the post-semicolon code as additional import names.

# Input
from os import \
    name; print(name)

# Before: corrupted output
from os import name, name;, print

# After: left as-is (mirrors skip_line() behavior for single-line semicolons)
from os import \
    name; print(name)

Root cause

collect_import_continuation merges continuation lines wholesale into import_string. For a backslash-continued import, this produced "from os import name; print(name)". Since strip_syntax strips \, (, ), , but not ;, just_imports ended up as ['name;', 'printname'] — garbage import names.

Fix

• isort/parse.py: After collect_import_continuation returns, check whether a semicolon was introduced by the continuation (present in import_string but absent from the original statement). If so, output the original lines unchanged via in_lines[statement_index - 1 : index], preserving indentation. This matches the existing skip_line() behaviour for the single-line equivalent from os import name; print(name).
• tests/unit/test_regressions.py: Added regression test.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.15%. Comparing base (5382895) to head (4223059).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2508   +/-   ##
=======================================
  Coverage   99.15%   99.15%           
=======================================
  Files          41       41           
  Lines        3068     3073    +5     
  Branches      665      666    +1     
=======================================
+ Hits         3042     3047    +5     
  Misses         14       14           
  Partials       12       12           

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