[Github] Bump CI Container clang Version to 21.1.1

This patch bumps the CI container version to the latest release version.
No particular reason to do this other than to ensure that we are using
a clang built with IRPGO now that has relanded for the slight
performance benefit.

Author: boomanaiden154

.github/workflows/containers/github-action-ci/Dockerfile

@@ -2,7 +2,7 @@ FROM docker.io/library/ubuntu:24.04 as base
 ENV LLVM_SYSROOT=/opt/llvm
 
 FROM base as stage1-toolchain
-ENV LLVM_VERSION=21.1.0
+ENV LLVM_VERSION=21.1.1
 
 RUN apt-get update && \
     apt-get install -y \