Update dirty_database.mdx (#813)

Update link from private sg/sg repo to sg/artifacts

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Author: morgangauth

docs/admin/how-to/dirty_database.mdx

@@ -80,7 +80,7 @@ ORDER BY version
 
 ### 2. Run the sql queries to finish incomplete migrations
 
-Migration definitions for each database schema can be found in the children of the [`migrations/` directory](https://github.com/sourcegraph/sourcegraph/tree/main/migrations).
+Migration definitions for each database schema can be found in the children of the [`migrations/` directory](https://github.com/sourcegraph/artifacts/tree/main/migrations).
 
 **Find the target migration with the version number identified in [step 1](#1-identify-incomplete-migration)**.