Update Dockerfile Ubuntu 24.04 to include clang

Author: shahmishal

swift-ci/master/ubuntu/24.04/Dockerfile

@@ -7,6 +7,7 @@ ENV DEBIAN_FRONTEND="noninteractive"
 
 RUN apt-get -y update && apt-get -y install \
   build-essential       \
+  clang                 \
   cmake                 \
   git                   \
   icu-devtools          \