bitcoin: poller: fix spend expiration from mempool, again #1530

Job	Run time
linter	1m 4s
linter_gui	5m 55s
unit_tests (1.54, ubuntu-latest)	5m 11s
unit_tests (1.54, macOS-latest)	17m 28s
unit_tests (1.54, windows-latest)	6m 54s
unit_tests (nightly, ubuntu-latest)	56s
unit_tests (nightly, macOS-latest)	1m 17s
unit_tests (nightly, windows-latest)	1m 37s
unit_tests_gui (1.65, ubuntu-latest)	6m 43s
unit_tests_gui (1.65, macOS-latest)	10m 59s
unit_tests_gui (1.65, windows-latest)	8m 52s
unit_tests_gui (nightly, ubuntu-latest)	2m 49s
unit_tests_gui (nightly, macOS-latest)	4m 0s
unit_tests_gui (nightly, windows-latest)	4m 58s
	1h 18m 43s

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