[sphinx.yml] work around orgs/community#25061

.github/workflows/sphinx.yml

@@ -7,6 +7,12 @@ jobs:
     runs-on: ubuntu-latest
     permissions:
       contents: write
+    defaults:
+      run:
+        shell: bash -el {0}
+        # GitHub configures `bash` to ignore ~/.bashrc and ~/.profile, but
+        # we can avoid this by using `bash -el {0}`
+        # see https://github.com/marketplace/actions/setup-miniconda and https://github.com/orgs/community/discussions/25061
     steps:
     - uses: actions/checkout@v4
     - name: Install Miniforge with dependencies