ci: fix bashism and ensure shell scripts are POSIX compliant
This is needed to support different shells and use alpine images in CI jobs
checkbashisms
and shellcheck
have been used to ensure scripts are compatible with sh
set -eux
has been consistently added across the scripts
-o pipefail
is not POSIX compliant but -e
cover most cases. lint.sh
could be the only one affected by this
there are a few additional style changes, eg: https://github.com/koalaman/shellcheck/wiki/SC2086