fix(core-flows): guest customer updates email to another guest account (#13037)

* fix(core-flows); guest customer updates email to another guest account

* wip: refactor test

* fix: refactor step, add testing

* fix: update test

* fix: string assertion in a test

.changeset/cool-nails-provide.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/core-flows": patch
+---
+
+fix(core-flows): guest email change to another guest email