Add remaining linter dependencies to CI base image

Summary: Needed for the land bot. See associated failure during one of the dry-runs: https://build.bitcoinabc.org/viewLog.html?buildId=69159&tab=buildLog&_focus=189#_state=70

Test Plan: Pull the base image and verify shellcheck and php-codesniffer are installed

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6380