Update mysql Docker tag to v9

| datasource | package | from | to  |
| ---------- | ------- | ---- | --- |
| docker     | mysql   | 5.7  | 9.6 |


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

Author: renovate[bot]

.github/workflows/continuous-integration.yml

@@ -33,7 +33,7 @@ jobs:
           job: ${{ matrix.job }}
     services:
       mysql:
-        image: mysql:5.7
+        image: mysql:9.6
         env:
           MYSQL_ROOT_PASSWORD: 'password'
           MYSQL_ROOT_HOST: '%'