Downgrade llhttp-ffi #294

Job	Run time
test-flaky (jruby-9.4, ubuntu-latest)	48s
test (ruby-3.1, ubuntu-latest)	24s
test (ruby-3.2, ubuntu-latest)	18s
test (ruby-3.0, ubuntu-latest)	19s
test (ruby-3.3, ubuntu-latest)	22s
lint	14s
	2m 25s

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