[refurb] Use UserString instead of non-existent UserStr

[nijel]

Summary

The class name is UserString, not a UserStr, see https://docs.python.org/3.9/library/collections.html#collections.UserString

Test Plan

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+5 -5 violations, +0 -0 fixes in 4 projects; 50 projects unchanged)

apache/airflow (+2 -2 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview --select ALL

- kubernetes_tests/test_base.py:45:26: FURB189 Subclassing `str` can be error prone, use `collections.UserStr` instead
+ kubernetes_tests/test_base.py:45:26: FURB189 Subclassing `str` can be error prone, use `collections.UserString` instead
- tests/utils/log/test_secrets_masker.py:317:54: FURB189 Subclassing `str` can be error prone, use `collections.UserStr` instead
+ tests/utils/log/test_secrets_masker.py:317:54: FURB189 Subclassing `str` can be error prone, use `collections.UserString` instead

langchain-ai/langchain (+1 -1 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

- libs/core/tests/unit_tests/stubs.py:7:14: FURB189 Subclassing `str` can be error prone, use `collections.UserStr` instead
+ libs/core/tests/unit_tests/stubs.py:7:14: FURB189 Subclassing `str` can be error prone, use `collections.UserString` instead

scikit-build/scikit-build-core (+1 -1 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

- src/scikit_build_core/settings/skbuild_model.py:31:27: FURB189 Subclassing `str` can be error prone, use `collections.UserStr` instead
+ src/scikit_build_core/settings/skbuild_model.py:31:27: FURB189 Subclassing `str` can be error prone, use `collections.UserString` instead

indico/indico (+1 -1 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

- indico/legacy/pdfinterface/latex.py:169:16: FURB189 Subclassing `str` can be error prone, use `collections.UserStr` instead
+ indico/legacy/pdfinterface/latex.py:169:16: FURB189 Subclassing `str` can be error prone, use `collections.UserString` instead

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
FURB189	10	5	5	0	0

[sbrugman]

Thanks!

[charliermarsh]

Thanks, whoops!