Only run conda test on one matrix element

.github/workflows/CI_conda.yml

@@ -27,9 +27,9 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        julia-version: ['1.5.0', '1.6.1', '1.7.1']
-        python-version: ['3.7', '3.8', '3.9']
-        os: ['ubuntu-latest', 'macos-latest', 'windows-latest']
+        julia-version: ['1.7.1']
+        python-version: ['3.9']
+        os: ['ubuntu-latest']
     
     steps:
       - uses: actions/checkout@v1.0.0