Fix inverted grep patterns in backdrop-mysql-client tests

- Replace grep -qiv with proper negation pattern (grep -qi || echo $? | grep 1)
- Fixes bug where grep -v on multi-line files always passes
- Aligns with codebase convention from backdrop-defaults example

Author: cursoragent

examples/backdrop-mysql-client/README.md

@@ -37,13 +37,13 @@ lando bee db-export --file=/tmp/bee-export.sql
 
 ```bash
 # Exported SQL should use MySQL dump format (not MariaDB)
-lando exec appserver -- cat /tmp/bee-export.sql | grep -qiv "MariaDB dump"
+lando exec appserver -- cat /tmp/bee-export.sql | grep -qi "MariaDB dump" || echo $? | grep 1
 ```
 
 ```bash
 # Should be able to export with db-export without SSL errors
 lando db-export --stdout > /tmp/lando-export.sql
-cat /tmp/lando-export.sql | grep -i "Dump" | grep -qiv "MariaDB"
+cat /tmp/lando-export.sql | grep -i "Dump" | grep -qi "MariaDB" || echo $? | grep 1
 ```
 
 ## Destroy tests