[Github] Add Zlib at build time to CI container

This patch adds zlib at build time to the CI container. This is needed to make
an lldb test pass that defaults to using the system lld if it is not explicitly
enabled in LLVM_ENABLE_PROJECTS.

Fixes #123479 (by fixing the proximal cause).

Author: boomanaiden154

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

@@ -13,7 +13,8 @@ RUN apt-get update && \
     ninja-build \
     python3 \
     git \
-    curl
+    curl \
+    zlib1g-dev
 
 RUN curl -O -L https://github.com/llvm/llvm-project/archive/refs/tags/llvmorg-$LLVM_VERSION.tar.gz && tar -xf llvmorg-$LLVM_VERSION.tar.gz