[Fix] CI: license check for black 26.3.1 + skip disk_cache test without diskcache

- Add black to liccheck.ini Authorized Packages (MIT-licensed).
- pytest.importorskip("diskcache") at top of test_disk_cache.py so
  the test skips cleanly when diskcache isn't installed (it's no longer
  pulled in by the dev group after the CVE-2025-69872 mitigation).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/code_coverage_tests/liccheck.ini

@@ -171,3 +171,4 @@ langgraph: >=1.0.10 # MIT License
 langgraph-prebuilt: >=1.0.8 # MIT License - https://github.com/langchain-ai/langgraph/blob/main/LICENSE
 pytest-rerunfailures: >=15.1 # MPL 2.0 license
 pytest-recording: >=0.13.4 # MIT license
+black: >=24.10.0 # MIT License - https://github.com/psf/black/blob/main/LICENSE

tests/test_litellm/caching/test_disk_cache.py

@@ -4,6 +4,8 @@ import tempfile
 
 import pytest
 
+pytest.importorskip("diskcache")
+
 sys.path.insert(0, os.path.abspath("../../.."))
 
 from litellm.caching.disk_cache import DiskCache