fix: typo that breaks release/release.sh (#7798)

Author: devjgm

CHANGELOG.md

@@ -99,7 +99,7 @@ The following libraries are now considered stable and complete:
 * [Secret Manager API](google/cloud/secretmanager/README.md) [[quickstart]](google/cloud/secretmanager/README.md)
 * [Cloud Tasks API](google/cloud/tasks/README.md) [[quickstart]](google/cloud/tasks/README.md)
 
-## [BigQuery](https://github.com/googleapis/google-cloud-cpp/blob/main/google/cloud/bigquery/README.md)
+### [BigQuery](https://github.com/googleapis/google-cloud-cpp/blob/main/google/cloud/bigquery/README.md)
 
 * feat(generator): add options support to generated clients ([#7683](https://github.com/googleapis/google-cloud-cpp/pull/7683))