Resolve "It's impossible to commit twice to the same branch"

What does this MR do?

This fixes #50584 (closed)

Notes:

• It does this by updating the UPDATE_FILE_AFTER_COMMIT to set lastCommitSha instead of lastCommit. It didn't look like lastCommit property for a file was being used.
• This is probably related to https://gitlab.com/gitlab-org/gitlab-ce/commit/3530274b13ec4f20731f9f98ea94dabe1494072d

What are the relevant issue numbers?

Closes #50584 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides