Update upmerge workflow to ignore config and body-end changes

[sk593]

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Description

We ignore certain files in the upmerge workflow that shouldn't get overwritten in edge. This was previously broken because we weren't resetting to the changes on edge. Instead, we were resetting to the changes after the merge.

Test run: https://github.com/sk593/radius-docs/actions/runs/11728935169/job/32673463501
Test branch with config/body-end changes: https://github.com/sk593/radius-docs/pull/3/files
Test PR opened from upmerge workflow (with no config/body-end changes): sk593#2

Issue reference