[flake8-use-pathlib] Stabilize invalid-pathlib-with-suffix (PTH210)

Summary
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Stabilizes PTH210. Tests and docs looked good.

Test Plan
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Mentioned in 1 open issue around Python 3.14 support (`"."` becomes a valid
suffix in 3.14). Otherwise no issues or PRs since 2024-12-12, 6 days after the
rule was added.

Author: ntBre

crates/ruff_linter/src/codes.rs

@@ -923,7 +923,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Flake8UsePathlib, "206") => (RuleGroup::Stable, rules::flake8_use_pathlib::rules::OsSepSplit),
         (Flake8UsePathlib, "207") => (RuleGroup::Stable, rules::flake8_use_pathlib::rules::Glob),
         (Flake8UsePathlib, "208") => (RuleGroup::Preview, rules::flake8_use_pathlib::violations::OsListdir),
-        (Flake8UsePathlib, "210") => (RuleGroup::Preview, rules::flake8_use_pathlib::rules::InvalidPathlibWithSuffix),
+        (Flake8UsePathlib, "210") => (RuleGroup::Stable, rules::flake8_use_pathlib::rules::InvalidPathlibWithSuffix),
 
         // flake8-logging-format
         (Flake8LoggingFormat, "001") => (RuleGroup::Stable, rules::flake8_logging_format::violations::LoggingStringFormat),