lib.fifo: fix reset handling of asynchronous FIFOs. #3364

Job	Run time
smoke (amaranth-lang/amaranth-boards)	53s
check-links	48s
smoke (amaranth-lang/amaranth-stdio)	38s
test (3.8)	3m 21s
document	53s
smoke (amaranth-lang/amaranth-soc)	57s
test (3.9)	3m 55s
test (3.10)	3m 42s
test (3.11)	2m 44s
test (3.12)	3m 15s
test (pypy-3.8)	5m 38s
test (pypy-3.9)	5m 38s
test (pypy-3.10)	6m 9s
test (3.13-dev)	4m 31s
publish-docs	6s
publish-docs-dev	0s
required	1s
publish-package	46s
publish-schemas	9s
publish-release	0s
	44m 4s

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