Merge pull request #114 from ruby/restore-llvm21

Try to build llvm-21 again

Author: hsbt

.github/workflows/publish.yml

@@ -32,8 +32,7 @@ jobs:
           - { os: 'focal', tag: 'gcc-7',  extras: 'g++-7' }
 
           - { os: 'noble', tag: 'clang-22',  extras: 'llvm-22' }
-          # clang-21/llvm-21 packages are not found now.
-          # - { os: 'noble', tag: 'clang-21',  extras: 'llvm-21' }
+          - { os: 'noble', tag: 'clang-21',  extras: 'llvm-21' }
           - { os: 'noble', tag: 'clang-20',  extras: 'llvm-20' }
           - { os: 'noble', tag: 'clang-19',  extras: 'llvm-19' }
           - { os: 'noble', tag: 'clang-18',  extras: 'llvm-18' }