Fix invalid pipeline build chain tag evaluation

Closes #40944

See merge request gitlab-org/gitlab-ce!15805

(cherry picked from commit 103269b9)

b30e0e06 Fix invalid pipeline build chain tag evaluation
ad3be46b Implement and use Gitlab::Ci::Pipeline::Chain::Command
865341ac Fix a bug of before_sha being inproperly evaluated to `checkout_sha`
b5f6a5f9 Add Chain::Command specs
99101f94 Fix Rubocop