Add alembic and imath dependencies to linux ci images. Exclude others.

.gitlab/ci/configure_el7_mindeps_python_qt5.cmake

.gitlab/ci/configure_el8_icc_python.cmake

.gitlab/ci/configure_macos.cmake

.gitlab/ci/configure_webassembly.cmake

.gitlab/ci/configure_wheel.cmake

.gitlab/ci/configure_windows.cmake

.gitlab/ci/docker/fedora34/Dockerfile

.gitlab/ci/docker/fedora34/install_alembic.sh

.gitlab/ci/docker/fedora34/install_imath.sh

.gitlab/os-linux.yml