fix: prevent multiple pvm errors on migration (apache#31332)

superset/migrations/shared/catalogs.py

@@ -505,7 +505,9 @@ def upgrade_schema_perms(
             .filter_by(name=current_perm)
             .one_or_none()
         ):
-            existing_pvm.name = new_perm
+            # check that new_perm does not exist
+            if not session.query(ViewMenu).filter_by(name=new_perm).one_or_none():
+                existing_pvm.name = new_perm
         elif new_perm:
             # new schema discovered, need to create a new permission
             perms[new_perm] = ("schema_access",)
@@ -683,7 +685,9 @@ def downgrade_schema_perms(
                 None,
                 schema,
             )
-            pvms_to_rename.append((pvm, new_name))
+            # check to see if the new name already exists
+            if not session.query(ViewMenu).filter_by(name=new_name).one_or_none():
+                pvms_to_rename.append((pvm, new_name))
         else:
             # non-default catalog, delete schema perm
             pvms_to_delete.append(pvm)