A redefinition of an attribute group restricts the original (src-redefine /
cos-ct-restricts), so it may not relax a fixed value the original sets. schM10
(changing a fixed attribute to a default one) is now rejected. The check fires
only when the redefinition declares the matching attribute as non-prohibited
with a differing fixed value; keeping the same fixed value, prohibiting it, or
omitting it is left alone, and it rides the existing namespaced base lookup, so
no valid redefinition is rejected.
XSTS invalid-schemas-accepted 65 -> 64, no false positive (valid-schemas-rejected
and valid-instances-rejected held at 0), no other bucket moved.