infra: Scope incremental cascade per parameter set (RedHatQE#5086)

##### What this PR does / why we need it:
When an incremental class is parametrized at class level, a failure in
one parameter set (e.g. ipv4) should not cascade into another (e.g.
ipv6) since they are independent test cycles with fresh fixtures.
This was discovered while working on PR RedHatQE#5026 — adding
`@pytest.mark.jira("CNV-88755", run=False)` to a single test caused 6
xfails instead of just 2 skips, because `_previousfailed` is stored on
the class node which is shared across all parametrize combinations.

##### Which issue(s) this PR fixes:

##### Special notes for reviewer:
- Non-parametrized incremental classes are unaffected — all their tests
share the same key so behavior is identical to before.
 - Currently two incremental classes use class-level parametrize:
-
`tests/network/l2_bridge/migration_stuntime/test_migration_stuntime.py`
- `tests/network/localnet/migration_stuntime/test_migration_stuntime.py`

##### jira-ticket:



<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Tests**
* Improved incremental test failure tracking for parametrized tests, so
failures are tracked per-parameter set—leading to clearer xfail
attribution and more reliable test outcomes.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Signed-off-by: Anat Wax <awax@redhat.com>

Author: Anatw

conftest.py

@@ -676,7 +676,10 @@ def pytest_runtest_makereport(item, call):
     """
     if call.excinfo is not None and "incremental" in item.keywords:
         parent = item.parent
-        parent._previousfailed = item
+        param_key = item.callspec.id if hasattr(item, "callspec") else ""
+        if not hasattr(parent, "_previousfailed"):
+            parent._previousfailed = {}
+        parent._previousfailed[param_key] = item
 
     outcome = yield
     report = outcome.get_result()
@@ -732,7 +735,8 @@ def pytest_runtest_setup(item):
     BASIC_LOGGER.info(f"\n{separator(symbol_='-', val=item.name)}")
     BASIC_LOGGER.info(f"{separator(symbol_='-', val='SETUP')}")
     if "incremental" in item.keywords:
-        previousfailed = getattr(item.parent, "_previousfailed", None)
+        param_key = item.callspec.id if hasattr(item, "callspec") else ""
+        previousfailed = getattr(item.parent, "_previousfailed", {}).get(param_key)
         if previousfailed is not None:
             pytest.xfail(f"previous test failed ({previousfailed.name})")