Rename RuleGroup::Unspecified to Stable (#7991)

Should help with #7989 and seems more accurate for our new model

crates/ruff_macros/src/map_codes.rs

@@ -58,7 +58,7 @@ pub(crate) fn map_codes(func: &ItemFn) -> syn::Result<TokenStream> {
     };
 
     // Map from: linter (e.g., `Flake8Bugbear`) to rule code (e.g.,`"002"`) to rule data (e.g.,
-    // `(Rule::UnaryPrefixIncrement, RuleGroup::Unspecified, vec![])`).
+    // `(Rule::UnaryPrefixIncrement, RuleGroup::Stable, vec![])`).
     let mut linter_to_rules: BTreeMap<Ident, BTreeMap<String, Rule>> = BTreeMap::new();
 
     for arm in arms {

scripts/add_rule.py

@@ -140,8 +140,7 @@ pub(crate) fn {rule_name_snake}(checker: &mut Checker) {{}}
         variant = pascal_case(linter)
         rule = f"""rules::{linter.split(" ")[0]}::rules::{name}"""
         lines.append(
-            " " * 8
-            + f"""({variant}, "{code}") => (RuleGroup::Unspecified, {rule}),\n""",
+            " " * 8 + f"""({variant}, "{code}") => (RuleGroup::Stable, {rule}),\n""",
         )
         lines.sort()
         text += "".join(lines)