Fix ignored gzip exit status in GZCompressAction

[sahvx655-wq]

GZCompressAction::execute currently waits for the spawned gzip process using apr_proc_wait, but discards the child process exit status by passing NULL for the exit code parameter.

As a result, failures from the compression process are not explicitly detected before execution continues. This behavior differs from ZipCompressAction::execute, which retrieves and validates the child process exit status.

This patch updates GZCompressAction::execute to capture the exit status returned by apr_proc_wait and validate it before proceeding, aligning its behavior with the existing implementation in ZipCompressAction.

Impact
Improves error handling consistency for compression actions and ensures that gzip process failures are not silently ignored.
Proposed Changes
Retrieve the child process exit status in GZCompressAction::execute.
Validate the returned exit status before continuing.
Align gzip compression handling with the existing ZipCompressAction implementation.

[swebb2066]

The are a number of usages of apr_proc_wait in the test cases as well. It would be appropriate to use SubProcessFailure::makeMessage it you are willing.

[sahvx655-wq]

I have updated the implementation to use SubProcessFailure for subprocess exit handling and pushed the changes for review.