filterx: fix memory leak of FilterXExpr->expr_text #1409

Job	Run time
create-source-tarball	1m 50s
create-packages / debian-bookworm	6m 10s
create-packages / debian-testing	6m 34s
create-packages / fedora-39	6m 36s
create-packages / ubuntu-jammy	8m 36s
	29m 46s

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