Update directory_writer.yml

Author: cclauss

Diff for: .github/workflows/directory_writer.yml

@@ -8,6 +8,8 @@ jobs:
     steps:
       - uses: actions/checkout@v1  # v1, NOT v2
       - uses: actions/setup-python@v2
+        with:
+          python-version: "3.10.0-beta.1"
       - name: Write DIRECTORY.md
         run: |
           scripts/build_directory_md.py 2>&1 | tee DIRECTORY.md