Upgrade from 2.23 does not finish

User impact:
User is not able to upgrade PMM 2.23 to dev-latest

Preconditions:

• Start PMM Server 2.23, and enable experimental repo by running:

docker exec pmm-server yum update -y percona-release
docker exec pmm-server sed -i -e 's^/release/^{/experimental/}' /etc/yum.repos.d/pmm2-server.repo
docker exec pmm-server percona-release enable percona experimental

Steps to reproduce:

1. open PMM and click Upgrade to 2.29
2. upgrade does not finish

Actual result:
The upgrade does not finish

Expected result:

User should be upgraded to dev-latest successfully