Backport of "Update VERSION file for 18.1.3-internal0"

What does this MR do and why?

This MR is a result of manually resolving a branch divergence from the security mirror. This includes pointing the VERSION file to the correct version number.

References

Screenshots or screen recordings

N/A

Before	After

How to set up and validate locally

N/A

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• The MR title is descriptive (e.g. "Backport of 'title of default branch MR'"). This is important, since the title will be copied to the patch blog post.
• This MR has a [severity label] assigned (if applicable). (previously added, but removing as it's N/A)
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:test-on-omnibus-ee job has either succeeded or been approved by a Software Engineer in Test.