create-spack-mirror CI tests failing 06/06/2022

The create-spack-mirror CI tests are now (06/06/2022) failing with
```
==> Warning: included configuration files should be updated manually [files=${SPACK_STACK_DIR}/configs/common/modules.yaml, ${SPACK_STACK_DIR}/configs/common/config.yaml, site, packages.yaml]
==> Error: Invalid url format from url: ${SPACK_STACK_DIR}/cache/source_cache
Error: Process completed with exit code 3.
```