Update .gitlab-ci.yml for 1.x branch to run D10 core

Problem/Motivation

The 1.x branch of this module is incompatible with D11, so only run tests against D10 core.

Proposed resolution

Update .gitlab-ci.yml for 1.x branch to run D10 core

Remaining tasks

Open MR

User interface changes

None

API changes

None

Data model changes

None