chore(iast): fix idna package test (#10377)

## Description

- Fix IDNA package test.
- Make the warning about a package that was marked as failing now
working a warning (xfail).

Signed-off-by: Juanjo Alvarez <[email protected]>

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

---------

Signed-off-by: Juanjo Alvarez <[email protected]>
Co-authored-by: Alberto Vara <[email protected]>

Author: juanjux

Diff for: tests/appsec/iast_packages/test_packages.py

@@ -290,7 +290,6 @@ def uninstall(self, python_cmd):
         "xn--eckwd4c7c.xn--zckzah",
         import_module_to_validate="idna.codec",
         test_propagation=True,
-        fixme_propagation_fails=False,
     ),
     PackageForTesting(
         "importlib-resources",
@@ -885,7 +884,7 @@ def _assert_propagation_results(response, package):
     if package.fixme_propagation_fails is not None:
         if result_ok:
             if package.fixme_propagation_fails:  # For packages that are reliably failing
-                pytest.fail(
+                pytest.xfail(
                     "FIXME: Test passed unexpectedly, consider changing to fixme_propagation_fails=False for package %s"
                     % package.name
                 )