fix(ci): pin celery (#2593)

* fix(ci): pin celery

Latest celery appears to be broken until
celery/celery#6829 is resolved.

* Disable other latest

* Get the versions right

Author: Kyle-Verhoog

riotfile.py

@@ -358,7 +358,9 @@ def select_pys(min_version=MIN_PYTHON_VERSION, max_version=MAX_PYTHON_VERSION):
                     },
                     pkgs={
                         "celery": [
-                            "~=5.0.5",
+                            # Pin until https://github.com/celery/celery/issues/6829 is resolved.
+                            # "~=5.0.5",
+                            "==5.0.5",
                             "~=5.0",  # most recent 5.x
                             latest,
                         ],