Revert "Pass the CI env in tox.ini and use it to conditionally skip tests on CI"

This reverts commit 000876e.

Author: ogrisel

testing/test_faulthandler.py

@@ -79,7 +79,7 @@ def test_timeout(pytester: Pytester, enabled: bool) -> None:
     If faulthandler is disabled, no traceback will be dumped.
     """
     if enabled and "CI" in os.environ:
-        pytest.skip(reason="sometimes crashes on CI (#7022)")
+        pytest.xfail(reason="sometimes crashes on CI (#7022)")
 
     pytester.makepyfile(
         """
@@ -110,7 +110,7 @@ def test_timeout():
 def test_timeout_and_exit(pytester: Pytester, exit_on_timeout: bool) -> None:
     """Test option to force exit pytest process after a certain timeout."""
     if "CI" in os.environ:
-        pytest.skip(reason="sometimes crashes on CI (#7022)")
+        pytest.xfail(reason="sometimes crashes on CI (#7022)")
 
     pytester.makepyfile(
         """

tox.ini

@@ -52,7 +52,6 @@ passenv =
     PYTEST_ADDOPTS
     TERM
     SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYTEST
-    CI
 setenv =
     _PYTEST_TOX_DEFAULT_POSARGS={env:_PYTEST_TOX_POSARGS_DOCTESTING:} {env:_PYTEST_TOX_POSARGS_LSOF:} {env:_PYTEST_TOX_POSARGS_XDIST:} {env:_PYTEST_FILES:}