fix: preserve GCC __attribute__ between enum keyword and name in AST

[Copilot]

__attribute__ placed between enum and the tag name (e.g. enum __attribute__((packed)) color { ... }) was silently dropped from the AST. The parser consumed the tokens correctly but discarded the returned attribute list instead of attaching it to the IASTEnumerationSpecifier.

Changes

• AbstractGNUSourceCodeParser.enumSpecifier() — capture the return value of __attribute_decl_seq() and call addAttributeSpecifiers(attributes, result) on the resulting enum specifier node, matching the pattern already used in classSpecifier() for struct/class/union
• AST2Tests.testEnumAttribute() — regression test verifying that enum __attribute__((packed)) color { ... } produces exactly one attribute specifier on the enum's decl specifier in the AST

// Previously: attribute was consumed but not added to the AST node
enum __attribute__ ((packed)) color {
    RED = 1,
    GREEN = 2
};

Checklist:

• Review contribution guidelines, particularly the Pull Request Flow
• Add an entry to New and Noteworthy for this releases
• Add an entry to API Changelog for any breaking changes
• Add an entry to API Changelog for future planned breaking changes
• Add an automated JUnit Plug-in test

[github-actions]

Test Results

4 719 tests  +1   4 710 ✅ +1   2m 30s ⏱️ -2s
  182 suites ±0       9 💤 ±0 
  182 files   ±0       0 ❌ ±0 

Results for commit 3869cdc. ± Comparison against base commit acd4556.

♻️ This comment has been updated with latest results.