chore(tests): unpin pytest

As the breaking change (deprecation) in pytest=8.1.1 has been already
fixed in flexmock¹, unpin pytest and also install flexmock from the PyPI
rather than RPM (to ensure the same behavior even if we switched back to
the CentOS images).

Newer version of pytest introduces ‹PYTEST_VERSION› environment variable
that can be used to detect whether the tests are being run or not, which
is used in some safe-guards in the events-refactor².

¹ flexmock/flexmock#153
² https://github.com/packit-service/packit/pull/2590

Signed-off-by: Matej Focko <[email protected]>

files/recipe-tests.yaml

@@ -8,15 +8,15 @@
     - name: Install test RPM dependencies
       ansible.builtin.dnf:
         name:
-          - python3-flexmock
           - tar
           - rsync
         state: present
     - name: Install pip deps
       ansible.builtin.pip:
         name:
           - requre
-          - pytest==8.0.2
+          - flexmock
+          - pytest
           - pytest-cov
           - pytest-flask
           - deepdiff < 8.0.0 # version 8.0.0 requires numpy, avoid it