Remove GitHub Workflow for mirroring to Gitlab

There was an advent recently, the Pipelines in Gitlab took a very long
time to execute, and used up my entire quota of free runners. At first
I thought of just adding timeouts, but then I thought there might be
better approaches to integrating with Gitlab.

So I'm removing the Gitlab integration for now, maybe in the future
when quotas are restored I'll set up a more convenient and thoughtful
integration again.

Author: xorcare

.github/workflows/gitlab.yml

@@ -2,8 +2,6 @@
 
 [![Go workflow status badge](https://github.com/xorcare/testing-go-code-with-postgres/actions/workflows/go.yml/badge.svg?branch=main)](https://github.com/xorcare/testing-go-code-with-postgres/actions/workflows/go.yml)
 [![codecov](https://codecov.io/github/xorcare/testing-go-code-with-postgres/branch/main/graph/badge.svg?token=AmPmVHf2ej)](https://codecov.io/github/xorcare/testing-go-code-with-postgres/tree/main)
-[![Gitlab CI Pipeline](https://gitlab.com/xorcare/testing-go-code-with-postgres/badges/main/pipeline.svg)](https://gitlab.com/xorcare/testing-go-code-with-postgres/tree/main)
-[![Gitlab CI Coverage](https://gitlab.com/xorcare/testing-go-code-with-postgres/badges/main/coverage.svg)](https://gitlab.com/xorcare/testing-go-code-with-postgres/tree/main)
 [![Go Report Card](https://goreportcard.com/badge/github.com/xorcare/testing-go-code-with-postgres)](https://goreportcard.com/report/github.com/xorcare/testing-go-code-with-postgres)
 
 The example suggests a solution to the problem of cleaning the database after