fix FiberError on LocalWorkflowContext#wait_until

[agiveygives]

When running tests in local mode on a workflow that contains a wait_until call, I was encountering the follow error:

E, [2025-03-04T14:13:47.126103 #82617] ERROR -- temporal_client: Workflow execution failed {"namespace":null,"workflow_id":"2c8e5d81-3ae6-47f9-8d33-ed8d6fd03253","workflow_name":"Workflow::MyWorkflow","workflow_run_id":"b0fe956d-8352-4ab6-b290-331e48fc2d93","parent_workflow_id":null,"parent_workflow_run_id":null,"attempt":1,"task_queue":"unit-test-task-queue","run_started_at":1741119227.09876,"memo":{},"error":"#<FiberError: attempt to yield on a not resumed fiber>"}
D, [2025-03-04T14:13:47.126150 #82617] DEBUG -- temporal_client: /Users/andrewgivens/.asdf/installs/ruby/3.4.2/lib/ruby/gems/3.4.0/bundler/gems/temporal-ruby-b5efd2cef802/lib/temporal/testing/local_workflow_context.rb:204:in 'Fiber.yield'
/Users/andrewgivens/.asdf/installs/ruby/3.4.2/lib/ruby/gems/3.4.0/bundler/gems/temporal-ruby-b5efd2cef802/lib/temporal/testing/local_workflow_context.rb:204:in 'Temporal::Testing::LocalWorkflowContext#wait_until'

I was able to fix the error and get my tests working with the patch in the PR that wraps the yield in a resumed Fiber