Revert "CI: Move the build stage to the project root instead of tmp (#47996)" (#48397)

This reverts commit ef615bcc.

share/spack/gitlab/cloud_pipelines/configs/config.yaml

@@ -7,6 +7,4 @@ config:
     padded_length: 256
     projections:
       all: '{architecture}/{compiler.name}-{compiler.version}/{name}-{version}-{hash}'
-  build_stage:
-  - $spack/tmp/stage