Only update lab if changed

The modified date for all labs is always being updated during the build even if the lab hasn't been updated.

This build pipeline should detect the changes since the last build (commit) and update changed labs only.

Start by locating the build pipeline that updates lab modified dates and inspect how it determines the current build commit. Compare the current commit with the previous build, then verify that unchanged labs retain their dates while changed labs are updated.

Written by the indexing model from the issue text.