remove python 3.7 version in test

Author: kailinzhuang

.github/workflows/dca_tests.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.7", "3.8", "3.9"]
+        python-version: ["3.8", "3.9"]
     steps:
       - name: Test DCA
         uses: actions/checkout@v4