docs: Fix a link in gitlab-ci.md

[SogoKato]

Description

An anchor link in https://aquasecurity.github.io/trivy/v0.43/tutorials/integrations/gitlab-ci/ is expired (#git-strategy does not exist in the page).

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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[knqyf263]

Thanks!