[ruff] Stabilize if-key-in-dict-del (RUF051) (#16658)

Summary
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Stabilizes RUF051. The tests and docs looked good.

Test Plan
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1 closed documentation issue from 4 days after the rule was added and 1
typo fix from the same day it was added, but no other issues or PRs.

Author: ntBre

crates/ruff_linter/src/codes.rs

@@ -1005,7 +1005,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         (Ruff, "047") => (RuleGroup::Preview, rules::ruff::rules::NeedlessElse),
         (Ruff, "048") => (RuleGroup::Stable, rules::ruff::rules::MapIntVersionParsing),
         (Ruff, "049") => (RuleGroup::Preview, rules::ruff::rules::DataclassEnum),
-        (Ruff, "051") => (RuleGroup::Preview, rules::ruff::rules::IfKeyInDictDel),
+        (Ruff, "051") => (RuleGroup::Stable, rules::ruff::rules::IfKeyInDictDel),
         (Ruff, "052") => (RuleGroup::Preview, rules::ruff::rules::UsedDummyVariable),
         (Ruff, "053") => (RuleGroup::Preview, rules::ruff::rules::ClassWithMixedTypeVars),
         (Ruff, "054") => (RuleGroup::Preview, rules::ruff::rules::IndentedFormFeed),