fix: compare against base branch instead of previous commit

Author: reuvenharrison

.github/workflows/pr-comment.yml

@@ -13,18 +13,10 @@ jobs:
     steps:
     - name: Check out code
       uses: actions/checkout@v4
-      with:
-        fetch-depth: 2
-
-    - name: Get prev commit
-      run: echo "PREV_COMMIT=$(git --no-pager log --skip=1 --max-count=1 | grep commit | cut -d' ' -f2)" >> $GITHUB_ENV
-
-    - name: Get prev file
-      run: echo "PREV_FILE=$(echo https://raw.githubusercontent.com/oasdiff/github-demo/${{ env.PREV_COMMIT }}/simple.yaml)" >> $GITHUB_ENV
 
     - name: Post oasdiff PR comment
       uses: oasdiff/oasdiff-action/pr-comment@main
       with:
-        base: ${{ env.PREV_FILE }}
+        base: https://raw.githubusercontent.com/${{ github.repository }}/${{ github.base_ref }}/simple.yaml
         revision: simple.yaml
         oasdiff-token: 0634345d-02fb-43df-b56a-68fc22253621