Bump gem version to correct one and add check

What does this MR do?

Fix incorrect gem version in main branch.

Add version check job in the test stage that prevents a changelog version bump without the same bump in the gem. Here are 2 execution with a failed and passing check:

• https://gitlab.com/gitlab-org/security-products/analyzers/license-finder/-/pipelines/362130273
• https://gitlab.com/gitlab-org/security-products/analyzers/license-finder/-/pipelines/362131414

Changelog entry is not necessary since this just changes the project's ci config.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Conforms to the code review guidelines