docs: Fix secret detection variable reference

Historic scan should reference the variables table for SD not SAST.

doc/user/application_security/secret_detection/index.md

@@ -258,7 +258,7 @@ want to perform a full secret scan. Running a secret scan on the full history ca
 especially for larger repositories with lengthy Git histories. We recommend not setting this CI/CD variable
 as part of your normal job definition.
 
-A new configuration variable ([`SECRET_DETECTION_HISTORIC_SCAN`](../sast/#vulnerability-filters))
+A new configuration variable ([`SECRET_DETECTION_HISTORIC_SCAN`](#available-variables))
 can be set to change the behavior of the GitLab Secret Detection scan to run on the entire Git history of a repository.
 
 We have created a [short video walkthrough](https://youtu.be/wDtc_K00Y0A) showcasing how you can perform a full history secret scan.