fix(ci): use ubuntu-20.04 for update workfow (#1370)

ubuntu-latest / 22.04 does not have python 3.6, use ubuntu-20.04 instead.

.github/workflows/update-dependencies.yml

@@ -18,7 +18,7 @@ jobs:
   update-dependencies:
     name: Update dependencies
     if: github.repository_owner == 'pypa' || github.event_name != 'schedule'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
     - uses: actions/checkout@v3