style: revert dedent block to flat form for black 26.1.0

My earlier local format pass used black 24.10.0 which expanded
``dedent(f"""...""")`` to a multi-line form; CI's ``tomte[black]==0.7.0``
pins black 26.1.0 which prefers the flat form. Restore the
pre-existing main-branch formatting so ``tox -e black-check`` passes.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: DIvyaNautiyal07

tests/test_skills/test_base.py

@@ -1215,8 +1215,7 @@ class TestSkillLoadingWarningMessages(BaseAEATestCase):
     _TEST_BEHAVIOUR_CLASS_NAME = "TestBehaviour"
 
     _test_skill_module_path = "skill_module_for_testing.py"
-    _test_skill_module_content = dedent(
-        f"""
+    _test_skill_module_content = dedent(f"""
     from aea.skills.base import Behaviour, Handler
 
     class {_TEST_HANDLER_CLASS_NAME}(Handler):
@@ -1240,8 +1239,7 @@ def act(self):
             pass
         def teardown(self):
             pass
-    """
-    )
+    """)
 
     @classmethod
     def setup_class(cls):