Update Ubuntu-arm.yml

Author: mcbarton

.github/workflows/Ubuntu-arm.yml

@@ -285,7 +285,7 @@ jobs:
           - name: ubu22-arm-gcc12-clang-repl-20
             os: ubuntu-22.04-arm
             compiler: gcc-12
-            clang-runtime: '19'
+            clang-runtime: '20'
             cling: Off
             cppyy: Off
           - name: ubu22-arm-gcc12-clang-repl-19-cppyy