Update mysql Docker tag to v9

| datasource | package | from | to |
| ---------- | ------- | ---- | -- |
| docker     | mysql   | 8    | 9  |


Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/continuous-integration.yml

@@ -25,7 +25,7 @@ jobs:
       mongo:
         image: mongo
       mysql:
-        image: mysql:8
+        image: mysql:9
         env:
           MYSQL_ROOT_PASSWORD: 'password'
           MYSQL_ROOT_HOST: '%'