conftest.py: Don't use deprecated get_marker() function

Starting from `pytest` version 4.1.0, `Node.get_marker()` has been
removed, and hence our tests break when running with newer versions of
`pytest`. It was deprecated since a while back but it has recently been
removed completely. Use `get_closest_marker()` as a replacement that is
suggested in the changelog, and seems to work fine for our use case.

See pytest-dev/pytest#4564 for more context on
the upstream issue.

One way of verifying this change is that this should fix the recently
added `tests-fedora-update-deps` job, that was failing before due to
this issue.

(cherry picked from commit c91784a)

conftest.py

@@ -30,7 +30,7 @@ def pytest_addoption(parser):
 
 
 def pytest_runtest_setup(item):
-    if item.get_marker('integration') and not item.config.getvalue('integration'):
+    if item.get_closest_marker('integration') and not item.config.getvalue('integration'):
         pytest.skip('skipping integration test')