fix: pin litellm upper bound to last tested version (1.82.6) (#5044)

The litellm optional dependency had a wide upper bound (<3) that allowed
any future litellm release to be installed automatically. This means
breaking changes in new litellm versions could affect customers immediately.

Pins the upper bound to <=1.82.6 (current latest known-good version).
When newer litellm versions are tested and validated, bump this bound
explicitly.

lib/crewai/pyproject.toml

@@ -83,7 +83,7 @@ voyageai = [
     "voyageai~=0.3.5",
 ]
 litellm = [
-    "litellm>=1.74.9,<3",
+    "litellm>=1.74.9,<=1.82.6",
 ]
 bedrock = [
     "boto3~=1.40.45",