Update deploy.yml

Fixed: https://github.com/pythonpune/readit/actions/runs/11255177655/job/31294163432
```
This request was automatically failed because there were no enabled runners online to process the request for more than 1 days.
The ubuntu-18.04 environment is deprecated, consider switching to ubuntu-20.04(ubuntu-latest), or ubuntu-22.04 instead. For more details see actions/runner-images#6002
```

.github/workflows/deploy.yml

@@ -10,7 +10,7 @@ on:
 jobs:
   build-and-publish:
     name: Build and publish readit distributions to PyPI
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     steps:
       - name: Checkout
         uses: actions/checkout@v2