fix(auth): test for proper mysql response

Because:

* We updated the local mysql to a version that doesn't pass auth-server
  tests.

This commit:

* Drops the local mysql to a version that the test passes.

Closes #FXA-6068.

_scripts/mysql.sh

@@ -22,7 +22,7 @@ docker run --rm --name=mydb \
   -e MYSQL_ROOT_HOST=% \
   -e MYSQL_DATABASE=pushbox \
   -p 3306:3306 \
-  mysql/mysql-server:8.0.30 --default-authentication-plugin=mysql_native_password &
+  mysql/mysql-server:8.0.28 --default-authentication-plugin=mysql_native_password &
 
 cd "$DIR"
 ./check-mysql.sh