Copy custom favicon to within the docs directory

The Material for MkDocs documentation says that the file must be within
the `docs` directory.

Reference: https://squidfunk.github.io/mkdocs-material/setup/changing-the-logo-and-icons/?h=#favicon

.github/workflows/fetch-and-compile-runtime-docs.yml

@@ -44,7 +44,7 @@ jobs:
         run: |
           mkdir -p _clones/microbiomedata/nmdc-runtime/assets/images/
           cp pullers/runtime_docs/mkdocs_overrides/main.html _clones/microbiomedata/nmdc-runtime/mkdocs_overrides/main.html
-          cp pullers/runtime_docs/assets/images/favicon.ico  _clones/microbiomedata/nmdc-runtime/assets/images/favicon.ico
+          cp pullers/runtime_docs/assets/images/favicon.ico  _clones/microbiomedata/nmdc-runtime/docs/assets/images/favicon.ico
       - name: Compile source documents into HTML
         #
         # References: