ci: Remove Poetry version pin

Remove a Poetry version pin to 1.2.2, which causes installation issues
on systems with Python 3.11.

The pin was originally introduced because Poetry 1.3 was deemed
unstable, due to the following bugs:

* #292 (comment)
* https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1029156

The first problem still stands, but we can circumvent it with the
`--no-ansi` flag, at no functionality cost. The second problem has been
resolved, but it never affected Ubuntu Focal in the first place.

Refs #292

.circleci/config.yml

@@ -151,10 +151,10 @@ jobs:
       - run:
           name: Install poetry dependencies
           command: |
-            # Remove this pin once the upstream Poetry issue is fixed:
+            sudo pip3 install poetry
+            # This flag is important, due to an open upstream Poetry issue:
             # https://github.com/python-poetry/poetry/issues/7184
-            sudo pip3 install poetry==1.2.2
-            poetry install
+            poetry install --no-ansi
       - run:
           name: Prepare cache directory
           command: |