CI: drop unnecessary work-around

pip in Debian stable works just fine.

Author: dnicolodi

.cirrus.yml

@@ -28,9 +28,6 @@ debian-11_task:
   container:
     dockerfile: ci/debian-11.docker
     cpu: 1
-  fix-pip_script:
-    # see https://github.com/pypa/pip/pull/11623
-    - python3 -m pip install --upgrade "pip @ git+https://github.com/pypa/pip.git@a057c9bc99ad7eab2e3b1539e79eee7d9a923f4f"
   << : *test
 
 debian-unstable_task: