Bump version from v1.3.0 -> v.1.3.1 (#40)

Prepare to release v1.3.1 of the xAI Python SDK following #39

Author: Omar-V2

src/xai_sdk/__about__.py

@@ -3,4 +3,4 @@
 # To change the version, do so using `uv run hatch version <new-version>`
 # or `uv run hatch version <patch|minor|major>` to bump the patch/minor/major version respectively.
 # See https://hatch.pypa.io/latest/version/#updating for more details.
-__version__ = "1.3.0"
+__version__ = "1.3.1"