update renovate.json to ignore pip requirements

By default, renovate's pip_requirements manager searches for all `requirements.txt`/`.pip` files (https://docs.renovatebot.com/modules/manager/pip_requirements/#default-config).  This PR adds an `ignorePaths` entry to ignore the default pattern, as described [here](https://docs.renovatebot.com/modules/manager/#ignoring-files-that-match-the-default-filematch).

renovate.json

@@ -13,6 +13,9 @@
       "schedule": null
     }
   },
+  "pip_requirements": {
+    "ignorePaths": "(^|/)([\\w-]*)requirements\\.(txt|pip)$"
+  },
   "packageRules": [
     {
       "matchPackagePatterns": ["ca-scribner-example-package", "^black$", "flake8", "pep8-naming", "isort", "codespell", "pytest"],