Drop the outdated torch versions in CI (#2830)

.github/workflows/merge_stage_test.yml

@@ -51,14 +51,12 @@ jobs:
     strategy:
       matrix:
         python-version: [3.7]
-        torch: [1.7.0, 1.8.0, 1.9.0]
+        torch: [1.8.1, 1.9.1]
         include:
-          - torch: 1.7.0
-            torchvision: 0.8.1
-          - torch: 1.8.0
-            torchvision: 0.9.0
-          - torch: 1.9.0
-            torchvision: 0.10.0
+          - torch: 1.8.1
+            torchvision: 0.9.1
+          - torch: 1.9.1
+            torchvision: 0.10.1
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python-version }}