Fix minify script parameters
Closes #1328 (closed)
We introduced a minor regression to the minify-assets script in this MR: !3291 (merged)
Adding the quotes around the $MINIFY_FLAGS
variable caused the script to parse the flags incorrectly, producing "unknown flag" warnings in the job output (example: https://gitlab.com/gitlab-org/gitlab-docs/-/jobs/3425143163#L3238).
Removing the quotes fixes the issue but still throws Shellcheck warnings. Unpacking the parameters from an array works fine and pleases Shellcheck, so let's go with that instead.