Add CAP_SYS_NICE to MySQL service config in GitHub Actions test workflow

.github/workflows/test.yml

@@ -157,7 +157,7 @@ jobs:
           MYSQL_DATABASE: wagtail
         ports:
           - 3306:3306
-        options: --health-cmd="mysqladmin ping" --health-interval=10s --health-timeout=5s --health-retries=3
+        options: --health-cmd="mysqladmin ping" --health-interval=10s --health-timeout=5s --health-retries=3 --cap-add=sys_nice
 
     steps:
       - uses: actions/checkout@v3