test: ts: access conversation epoch through transaction

previously this used the session to access the keystore. Since we didn't
initialize it this doesn't work anymore. We can use the transaction
which knows the keystore.
This is a design flaw overall. We have to discuss the best practice
here. It would make sense to move getters to the CC instance which is
how it is in the FFI layer.

Author: fewerner

crypto-ffi/bindings/js/test/wdio/database.test.ts

@@ -180,11 +180,13 @@ describe("database", () => {
             );
 
             const instance = await window.ccModule.CoreCrypto.init(database);
-            const epoch = await instance.conversationEpoch(
-                new window.ccModule.ConversationId(
-                    encoder.encode("convId").buffer
-                )
-            );
+            const epoch = await instance.transaction(async (ctx) => {
+                return await ctx.conversationEpoch(
+                    new window.ccModule.ConversationId(
+                        encoder.encode("convId").buffer
+                    )
+                );
+            });
             return epoch;
         }, JSON.stringify(stores));