upload codecov results in action.

Author: sbillinge

.github/workflows/main.yml

@@ -45,10 +45,16 @@ jobs:
           conda install --file requirements/run.txt
           conda install --file requirements/test.txt
           pip install -e .
+          
       - name: Validate diffpy.structure
         shell: bash -l {0}
         run: |
           conda activate test
           coverage run -m diffpy.structure.tests.run
           coverage report -m
           codecov
+          
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v4
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}