env/linux-x86-bullseye: add zlib1g to dependencies to install

This dependency is required for clang's llvm-symbolizer to decompress
DWARF debug information in the binaries we (and clang) produce. This is
already accounted for indirectly with the debian package manually
included for linux-x86-clang, but in the LUCI world, I chose to add
clang to CIPD so it's easier to update.

Fixes golang/go#65469.

Change-Id: Id58fb754f959c1a3b6da1b7505003697685a3b45
Reviewed-on: https://go-review.googlesource.com/c/build/+/561595
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

env/linux-x86-bullseye/Dockerfile

@@ -30,6 +30,7 @@ ENV DEBIAN_FRONTEND noninteractive
 # strace: optionally used by some net/http tests
 # subversion: subversion VCS supported by cmd/go
 # swig: used for c/c++ interop related tests
+# zlib1g: used for ASAN symbolization with clang
 RUN apt-get update && apt-get install -y \
 	--no-install-recommends \
 	bzr \
@@ -60,6 +61,7 @@ RUN apt-get update && apt-get install -y \
 	subversion \
 	sudo \
 	swig \
+	zlib1g \
 	&& rm -rf /var/lib/apt/lists/*
 
 RUN mkdir -p /go1.4-amd64 \