chore: change target of release candidates to private index

Pypi doesn't accept external dependencies so we need to change the
target of our release candidates this they will use Concrete Python's
versions that are not hosted on pypi anymore.

.github/workflows/release.yaml

@@ -308,6 +308,7 @@ jobs:
       PIP_EXTRA_INDEX_URL: ${{ secrets.PIP_EXTRA_INDEX_URL }}
       GIT_TAG: ${{ needs.release-checks.outputs.git_tag }}
       PROJECT_VERSION: ${{ needs.release-checks.outputs.project_version }}
+      IS_RC: ${{needs.release-checks.outputs.is_rc}}
 
     # Jobs are separated runners, we therefore need to install dependencies again in order to
     # pursue (without using cache or upload/download them as artifacts)
@@ -584,17 +585,17 @@ jobs:
           docker image push --all-tags "${PUBLIC_RELEASE_IMAGE_BASE}"
 
       - name: Push package to PyPi
-        if: ${{ success() && !cancelled() }}
+        if: ${{ (env.IS_RC == 'false') && success() && !cancelled() }}
         run: |
           poetry run twine upload \
           -u __token__ -p ${{ secrets.PYPI_BOT_TOKEN }} \
           -r pypi "${{ env.ARTIFACTS_PACKAGED_DIR }}"/*.whl
 
-      # This step is kept if Concrete ML starts to publish private nightly release one day. For now,
-      # since release candidates and actual releases are public, we don't need to publish anything
-      # to the private internal repo
+      # Release candidates are pushed to the internal pypi
+      # because it depends on the internal builds of Concrete Python
+      # and pypi doesn't allow external dependencies.
       - name: Push package to Internal PyPi
-        if: false
+        if: ${{ env.IS_RC == 'true' }}
         run: |
           poetry run twine upload \
           -u "${{ secrets.INTERNAL_PYPI_BOT_USERNAME }}" -p "${{ secrets.INTERNAL_PYPI_BOT_PASSWORD }}" \