Integrate gitlab-ci/add_git_credentials_script and 2 more

Commit: seco-ne/yocto/infrastructure/gitlab-ci@42bfe4f0

build:prepare: Add setup script for Git Credentials

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@24653ff8

build:machines: Add i.MX93 to the build job template

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Commit: seco-ne/yocto/infrastructure/gitlab-ci@7aae72ea

Re-enable sourcery

With the free open source plan, sourcery works only when called from the repository's root directory. Re-enable it by calling it from there.

Also apply sourcery's suggestions to file generate_firmware_package.py, which did not exist before disabling sourcery.