fix a bug of chart e2e workflow (#242)

Signed-off-by: Yingchun Guo <yingchun.guo@intel.com>

.github/workflows/chart-e2e.yaml

@@ -30,15 +30,18 @@ jobs:
         uses: actions/checkout@v4
         with:
           ref: "refs/pull/${{ github.event.number }}/merge"
+          fetch-depth: 0
 
       - name: Get test matrix
         id: get-test-matrix
         run: |
-          e2e_charts=$(git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }} | \
+          base_commit=${{ github.event.pull_request.base.sha }}
+          merged_commit=$(git log -1 --format='%H')
+          e2e_charts=$(git diff --name-only ${base_commit} ${merged_commit} | \
           grep "^$CHARTS_DIR/" | \
           grep -vE 'README.md|common|*.sh' | \
           cut -d'/' -f2 | sort -u )
-          common_charts=$(git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }} | \
+          common_charts=$(git diff --name-only ${base_commit} ${merged_commit} | \
           grep "^$CHARTS_DIR/common" | \
           grep -vE 'README.md|*.sh' | \
           cut -d'/' -f3 | sort -u )