Keep lint checks compatible with supported Python 3.8

[xiehuanyi]

The tox matrix includes Python 3.8, but Ruff has no target-version setting. Its current default reports 5 B905 violations suggesting zip(..., strict=...), a keyword unavailable on Python 3.8. The prescribed format check also fails on two adjacent string literals.

Set Ruff's target to the oldest Python version in the tox matrix. Join only the two literals required by the format check; their exact string values are unchanged. This lets the prescribed lint and formatting checks pass without introducing unsupported syntax or changing runtime behavior.

Validation: unchanged base has 5 lint errors and 2 files failing formatting. After the three-file correction, tox run -e rufflint,ruffformatcheck passes both environments with 27 files formatted. All 58 SortedDict tests pass, exact literal-value equality was verified, and git diff --check passes.

Prepared with AI assistance.

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