[CI] Remove clang 8.

Author: mjpt777

.github/workflows/ci.yml

@@ -145,7 +145,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        version: [ '8', '9', '10', '11', '12', '13', '14' ]
+        version: [ '9', '10', '11', '12', '13', '14' ]
     env:
       CC: clang-${{ matrix.version }}
       CXX: clang++-${{ matrix.version }}