.gitlab-ci.yml: use explicit dependency on pi4 bundle build job

This allows the bundle job to be started even if just one of the jobs
in the previous stage, the one for pi4 image build, succeeds. This is
better for testing and allows jobs to start and finish faster, reducing
total build time.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>