Update begin-after-commit-hash (#92)

The generated client in this library was recently updated so the `begin-after-commit-hash` should match the SHA of the update:

The following changes were pulled in:
feat: Added support for configurable budget time period.
fix: Updated some documentation links.

.github/.OwlBot.yaml

@@ -22,5 +22,5 @@ deep-copy-regex:
   - source: /google/cloud/billing/budgets/(v.*)/.*-py/(.*)
     dest: /owl-bot-staging/$1/$2
 
-begin-after-commit-hash: 6a5da3f1274b088752f074da5bc9e30bd1beb27e
+begin-after-commit-hash: 0a3c7d272d697796db75857bac73905c68e498c3