[flake8-import-conventions] Document that extend-aliases can override default aliases

[LHMQ878]

Closes #17097

Summary

The extend-aliases documentation only stated that entries "will be added to the aliases
mapping", which does not convey that an entry for a module that already has a default alias
replaces that default. As noted in the issue, this makes it possible to change or opt out
of a default alias without restating the whole aliases mapping.

This is a documentation-only change; the behaviour already works this way because the
settings resolver applies extend-aliases on top of aliases via HashMap::extend, so
matching keys are overwritten.

Test Plan

Verified the documented behaviour against ruff 0.12.4 using this sample file:

import numpy
import numpy as np

Config	Result
default	ICN001 numpyshould be imported asnp`` on line 1
numpy = "numpy" under extend-aliases	ICN001 numpyshould be imported asnumpy`` on line 2, i.e. the aliased import is now the violation
numpy = "nmp" under extend-aliases	both lines flagged, requiring nmp, so the default np is fully replaced

Also ran:

• cargo fmt --check - passes.
• cargo dev generate-all - regenerated ruff.schema.json so the new description is
  reflected there; confirmed the file is still valid JSON and contains the updated text.

[ntBre]

Thanks. As I noted on the issue, I'm not sure this is really an intended usage that we want to point users toward. I think I would make the minimal change necessary to acknowledge that this works, which would be something like:

 /// A mapping from module to conventional import alias. These aliases will
 /// be added to the [`aliases`](#lint_flake8-import-conventions_aliases) mapping
+/// and will override any existing `aliases` if the two settings overlap.

[LHMQ878]

Makes sense — reduced to exactly your suggested wording in 47b31fb.

Dropped the paragraph about using a self-alias to opt out of a default, and the numpy = "numpy" example line with it, so the docs no longer point anyone toward that usage. ruff.schema.json is regenerated from the doc comment, hence the second file.

The diff is now the one-liner you wrote, nothing else.

[astral-sh-bot]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.