Fix initialization of defaults in yaml schema validation (#7959)

Fixes #7924

Spack's yaml schema validator was initializing all instances of
unspecified properties with the same object, so that updating the
property for one entry was updating it for others (e.g. updating
versions for one package would update it for other packages).

This updates the schema validator to instantiate defaults with
separate object instances and adds a test to confirm this behavior
(and also confirms #7924 without this change).

0 files changed, 0 insertions, 0 deletions