fix(deferred): add EXIT_CODE to deferred tasks

[NikitaCOEUR]

Fixes #1966

This pull request includes changes to enhance the handling of deferred commands and variables in tasks, as well as updates to the corresponding tests and task configuration files. The most important changes include adding support for variable substitution in deferred commands.

Enhancements to deferred commands:

• task.go: Added logic to handle variable substitution for the Value and Sh fields in deferred tasks. This ensures that variables are correctly replaced with their values before the command is executed.

Updates to tests:

• task_test.go: Added new test cases to verify that deferred commands with variable substitution are executed correctly, including handling of EXIT_CODE and other dynamic values.

Updates to task configuration:

• testdata/deferred/Taskfile.yml: Updated the task configuration to include examples of deferred commands with variable substitution, demonstrating the new functionality and ensuring comprehensive test coverage.