internal/postgres: change ON CONFLICT key in insertLicenses

insertLicenses now uses licenses (module_id, file_path) as the ON
CONFLICT key.

For golang/go#39629

Change-Id: Ib85a61f538a176c1bfff7a070121162405ef21dc
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/265241
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>

internal/postgres/insert_module.go

@@ -227,7 +227,7 @@ func insertLicenses(ctx context.Context, db *database.DB, m *internal.Module, mo
 			"module_id",
 		}
 		return db.BulkUpsert(ctx, "licenses", licenseCols, licenseValues,
-			[]string{"module_path", "version", "file_path"})
+			[]string{"module_id", "file_path"})
 	}
 	return nil
 }