fix(test): pass explicit did to seedWebhook in CRUD test

The webhook CRUD test combined an explicit did:plc:user webhook
with seedWebhook calls that defaulted to did:plc:test, so
listWebhooksByDid("did:plc:user") only returned the one
explicit row instead of three.

tests/db_test.ts

@@ -99,8 +99,16 @@ Deno.test(
     assertEquals(created.token, undefined);
     assertEquals(created.url, "https://example.com/a");
 
-    seedWebhook({ url: "https://example.com/b", verb: "create" });
-    seedWebhook({ url: "https://example.com/c", verb: "delete" });
+    seedWebhook({
+      did: "did:plc:user",
+      url: "https://example.com/b",
+      verb: "create",
+    });
+    seedWebhook({
+      did: "did:plc:user",
+      url: "https://example.com/c",
+      verb: "delete",
+    });
 
     const list = listWebhooksByDid("did:plc:user");
     assertEquals(list.length, 3);