Add an option to download packcheck in `run-ci.sh`

[adithyaov]

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For my shell, I had to replace packcheck.sh with ./packcheck.sh in run-ci.sh to work. We can download it to a temporary location and get the absolute path.

[harendra-kumar]

Downloading it in this script is a very heavy solution for this. This script assumes you have packcheck.sh in your PATH. Add the script location in your PATH, and it will work.