fix: outgoing transaction wrong callback update

Merged Nicolas Delpech requested to merge backport/outgoingtransaction_double_free into release/2.3

This could cause a free to be made on memory not owned anymore. This could happen in case of networking errors.

Add a test to ensure that the double free could not happen anymore.

(cherry picked from commit 792cdc3d)

FLEXISIP-385

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