change severity of G-3160 to blocker

because structural changes may lead to a bug

Author: PhilippSalvisberg

docs/4-language-usage/3-dml-and-sql/1-general/g-3160.md

@@ -1,6 +1,6 @@
 # G-3160: Avoid visible virtual columns.
 
-!!! warning "Major"
+!!! bug "Blocker"
     Maintainability, Reliability
 
 !!! missing "Unsupported in db\* CODECOP Validators"