fix: reduce release-please search depth from 500 to 50

release-please defaults to walking 500 commits and 400 releases on
every run, making each API call per-commit. With ~20 commits between
releases, this wastes ~2 minutes on unnecessary GitHub API calls.

.github/release-please-config.json

@@ -1,6 +1,8 @@
 {
   "$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
   "include-component-in-tag": true,
+  "release-search-depth": 20,
+  "commit-search-depth": 50,
   "packages": {
     ".": {
       "release-type": "simple",