try llvm8 manual install

Author: ladyada

actions_install.sh

@@ -4,6 +4,7 @@ set -e
 
 pip3 install clint pyserial setuptools adafruit-nrfutil
 sudo apt-get update
+sudo apt-get install -y libllvm8
 sudo apt install -fy cppcheck clang-format-8
 sudo ln -s /usr/bin/clang-format-8 /usr/bin/clang-format