ci: clean conda cache before building the packages

The `actual` sha256 hashes match both what I calculate by downloading and running `sha256sum` and what is posted on conda-forge.

I suspect then that our build is using some bad cached value as the "expected".

conda-forge: https://conda.anaconda.org/conda-forge/noarch/

Ref: apache#659

.github/workflows/conda.yml

@@ -81,6 +81,9 @@ jobs:
           which python
           pip list
           mamba list
+      # Clean the conda cache
+      - name: Clean Conda Cache
+        run: conda clean --all --yes
       - name: Build conda packages
         run: |
           # suffix for nightly package versions