MNT: Update codecov-action version to v2

Author: pllim

.github/workflows/ci_tests.yml

@@ -72,7 +72,7 @@ jobs:
       run: tox ${{ matrix.toxargs }} -e ${{ matrix.toxenv }} -- ${{ matrix.toxposargs }}
     - name: Upload coverage to codecov
       if: contains(matrix.toxenv,'-cov')
-      uses: codecov/codecov-action@v1
+      uses: codecov/codecov-action@v2
       with:
         file: ./coverage.xml