[R][CI] rhub/ubuntu-clang fails on missing libpng

[rok]

Describe the bug, including details regarding any error messages, version, and platform.

test-r-linux-as-cran is failing in the rhub/ubuntu-clang matrix job.

png.h file not found
libpng-config: command not found

Proposed diff:

diff --git a/ci/scripts/r_install_system_dependencies.sh b/ci/scripts/r_install_system_dependencies.sh
@@
-    apt-get install -y libcurl4-openssl-dev libssl-dev libuv1-dev
+    apt-get install -y libcurl4-openssl-dev libpng-dev libssl-dev libuv1-dev

Component(s)

R