chore: migrate license from PMPL-1.0-or-later to MPL-2.0

Author: hyperpolymath

contractiles/k9/examples/project-metadata.k9.ncl

@@ -40,7 +40,7 @@ K9!
       organization = "The Open University",
     },
 
-    license = "PMPL-1.0-or-later",
+    license = "MPL-2.0",
 
     keywords = [
       "rhodium-standard",