Object of class `FunctionType` has no attribute `return_value` [missing-attribute]

[asukaminato0721]

Describe the Bug

in pytest env, we can set .return_value to change the return value.

https://github.com/langgenius/dify/pull/39876/changes#diff-11f51968a981aae553847d0824bf7e3f0750f5c1145432e57ec7c55eb727b216L157

But this causes some false positive.

Sandbox Link

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(Only applicable for extension issues) IDE Information

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