[pyproject] Upper pin pydantic until issue #31 is fixed

pyproject.toml

@@ -41,6 +41,7 @@ dependencies = [
   "torch>=1.8",
   "torchvision>=0.10",
   "lightning>=2.0.3",
+  "pydantic <2.0,>=1.7.4",  # temporary, until issue #31 is fixed
   "tensorboard",
 ]