Restrict pydantic to ~=2.9

Pydantic 2.8 doesn't have "core_schema.ComplexSchema"
needed in the current code. Let's support Pydantic 2.8
only when needed

pyproject.toml

@@ -50,6 +50,7 @@ python = "3.9"
 dependencies = [
   "aind-data-schema>=0.38.6",
   "dandischema>=0.10.2",
+  "pydantic~=2.9",
   "pytest",
   "pytest-cov",
   "pytest-mock",