.readthedocs.yml: bump Python to 3.10

Latest docs build failed https://readthedocs.org/projects/squad/builds/23864172/

```
Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/squad/envs/latest/lib/python3.7/site-packages/sphinx/config.py", line 350, in eval_config_file
    exec(code, namespace)
  File "/home/docs/checkouts/readthedocs.org/user_builds/squad/checkouts/latest/doc/conf.py", line 23, in <module>
    from squad.version import __version__
  File "/home/docs/checkouts/readthedocs.org/user_builds/squad/checkouts/latest/squad/__init__.py", line 10, in <module>
    raise e
  File "/home/docs/checkouts/readthedocs.org/user_builds/squad/checkouts/latest/squad/__init__.py", line 7, in <module>
    from .celery import app as celery_app  # noqa
  File "/home/docs/checkouts/readthedocs.org/user_builds/squad/checkouts/latest/squad/celery.py", line 9, in <module>
    from celery import Celery
ImportError: cannot import name 'Celery' from 'celery' (/home/docs/checkouts/readthedocs.org/user_builds/squad/envs/latest/lib/python3.7/site-packages/celery/__init__.py)
```

Which seems like it's a Python issue

Signed-off-by: Charles Oliveira <[email protected]>

.readthedocs.yml

@@ -6,7 +6,7 @@ version: 2
 build:
   os: ubuntu-22.04
   tools:
-    python: "3.7"
+    python: "3.10"
 sphinx:
   configuration: doc/conf.py
 formats: all