release: bump pyproject.toml to 0.5.3

The Python __init__.py version was already 0.5.3 (matching the npm
package.json) but pyproject.toml was missed in the release PR. Without
this bump, `pip install getpatter==0.5.3` would 404 on PyPI even after
the release.yml tag-push publish runs.

Author: nicolotognoni

sdk-py/pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "getpatter"
-version = "0.5.2"
+version = "0.5.3"
 description = "Open-source voice AI SDK — connect any AI agent to real phone calls in 4 lines of code"
 readme = "README.md"
 license = { text = "MIT" }