Update uselagoon/mysql-8.4 Docker tag to v26.4.0

| datasource | package             | from   | to     |
| ---------- | ------------------- | ------ | ------ |
| docker     | uselagoon/mysql-8.4 | 26.3.0 | 26.4.0 |

Author: Renovate Self Hosted

docker-compose.yml

@@ -186,7 +186,7 @@ services:
       context: .
       dockerfile: .docker/database.dockerfile
       args:
-        IMAGE: "${VORTEX_DB_IMAGE:-uselagoon/mysql-8.4:26.3.0}" # Use custom database image (if defined) or fallback to standard database image.
+        IMAGE: "${VORTEX_DB_IMAGE:-uselagoon/mysql-8.4:26.4.0}" # Use custom database image (if defined) or fallback to standard database image.
     environment:
       <<: *default-environment
     <<: *default-user
@@ -199,7 +199,7 @@ services:
 
   #;< MIGRATION
   database2:
-    image: "${VORTEX_DB2_IMAGE:-uselagoon/mysql-8.4:26.3.0}" # Use custom database image (if defined) or fallback to standard database image.
+    image: "${VORTEX_DB2_IMAGE:-uselagoon/mysql-8.4:26.4.0}" # Use custom database image (if defined) or fallback to standard database image.
     environment:
       <<: *default-environment
       MYSQL_DATABASE: drupal