ci: Relicense the CI scripts to the Boost Software License version 1.0

Fetch LICENSE_BSL_1_0.txt from http://www.boost.org/LICENSE_1_0.txt
and update the copyright notice in all ci_* scripts.

Append "SPDX-License-Identifier" tags after each copyright notice;
see https://github.com/david-a-wheeler/spdx-tutorial/#spdx-tutorial
4 files changed