Ensure we get the right diff to update knowledge base

[AnushaFF]

Description

When the GitHub Action runs on the main branch after a merge, the script was comparing origin/main to HEAD. But since the code had already been merged to main, HEAD was pointing to the same commit as origin/main, resulting in zero detected changes. This PR updates the diff detection logic

[Copilot]

Pull request overview

This PR fixes a critical issue in the GitHub Actions workflow where no file changes were being detected when running on the main branch after a merge. The solution introduces dynamic base commit detection using the GITHUB_BASE_SHA environment variable, which references the commit before the merge, ensuring proper diff detection.

Key Changes:

• Modified update_docs.py to use GITHUB_BASE_SHA environment variable for diff comparison when available, falling back to origin/main for local development
• Updated the workflow to fetch full Git history and pass the pre-merge commit SHA via github.event.before

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
update_docs.py	Updated diff logic to use GITHUB_BASE_SHA environment variable instead of hardcoded origin/main
.github/workflows/update-docs-prod.yml	Added full history fetch and set GITHUB_BASE_SHA to github.event.before for proper commit comparison

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