[BUG] Optional type transform not working in dynamic workflow

[jganbat-fn]

Describe the bug

Optional type transformation on output is not working during dynamic workflow compilation.

Following example workflow:

from __future__ import absolute_import, division, print_function
from typing import Optional

from flytekit import task, workflow, dynamic
from flytekit.types.file import FlyteFile

@task
def hello(myfile: Optional[FlyteFile]) -> Optional[FlyteFile]:
    return None

@dynamic
def dyn_hello(myfile: Optional[FlyteFile]) -> Optional[FlyteFile]:
    return hello(myfile=myfile)


@workflow
def child_workflow(myfile: Optional[FlyteFile]) -> Optional[FlyteFile]:
    hello_output = dyn_hello(myfile=myfile)
    return hello_output

when executed showing the following issue in FlytePropeller

E0601 21:21:14.327422       1 workers.go:102] error syncing 'flyte-sandbox/anwfrlcbl62scwxzsnh7': 0: [User] malformed dynamic workflow, caused by: Collected Errors: 2
	Error 0: Code: MismatchingTypes, Node Id: end-node, Description: Variable [o1] (type [union_type:<variants:<blob:<> structure:<tag:"FlyteFilePath" > > variants:<simple:NONE structure:<tag:"none" > > > ]) doesn't match expected type [union_type:<variants:<blob:<> > variants:<simple:NONE > > ].
	Error 1: Code: ParameterNotBound, Node Id: end-node, Description: Parameter not bound [o1].

Flytekit version: v1.4
Flytepropeller version: v1.1.91

Expected behavior

Optional output type is correctly transformed and routed to downstream tasks or returned.

relevant slack conversation is here https://flyte-org.slack.com/archives/CP2HDHKE1/p1685654534312309

Additional context to reproduce

Register and run the example workflow described above in sandbox.

Screenshots

No response

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• Yes

Have you read the Code of Conduct?

• Yes