chore(python): exclude setup.py in renovate config (#1570)

We're planing to migrate from a handwritten setup.py to an autogenerated one and will maintain `setup.py` in the generator itself.

Author: parthea

synthtool/gcp/templates/python_library/renovate.json

@@ -5,7 +5,7 @@
     ":preserveSemverRanges",
     ":disableDependencyDashboard"
   ],
-  "ignorePaths": [".pre-commit-config.yaml", ".kokoro/requirements.txt"],
+  "ignorePaths": [".pre-commit-config.yaml", ".kokoro/requirements.txt", "setup.py"],
   "pip_requirements": {
     "fileMatch": ["requirements-test.txt", "samples/[\\S/]*constraints.txt", "samples/[\\S/]*constraints-test.txt"]
   }