Gitlab Commit Status Publisher SSL error

I have standard Teamcity server and agent in Docker from official repo, I have configured Publish Status to gitlab which is on https and I every time got error (int teamcity-server.log): 

Publish status error in build #18c56c4f8f34eef77c40513df4d2aecbba256fee {build id=2533, buildTypeId=...}: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

Google helps me nothing. Every topic is about connecting TO teamcity server, not FROM it.

The cert on my gitlab site is working and trusted (from Avast)

BTW, the request to gitlab comes from Server or Agent?