eth/filters: fix failing benchmark-test

[holiman]

This PR fixes a benchmark-test which was made br0kken by this commit: https://github.com/ethereum/go-ethereum/pull/25641/files#diff-dcfcc1778e0f2ab8820d4b00af81d5ce5209067a3a9b40af012d9d07b641a8e1R59 .

Without this PR:

[user@work go-ethereum]$ go test -run - -bench BenchmarkFilters  ./eth/filters
INFO [11-09|08:44:00.421] Allocated cache and file handles         database=/tmp/BenchmarkFilters672625565/001 cache=16.00MiB handles=16
INFO [11-09|08:44:00.423] Persisted trie from memory database      nodes=1 size=142.00B time="5.708µs" gcnodes=0 gcsize=0.00B gctime=0s livenodes=1 livesize=0.00B
--- FAIL: BenchmarkFilters
    filter_test.go:94: expected 4 logs, got 0
FAIL
exit status 1
FAIL    github.com/ethereum/go-ethereum/eth/filters     5.455s
FAIL

With this PR:

[user@work go-ethereum]$ go test -run - -bench BenchmarkFilters  ./eth/filters
INFO [11-09|08:46:50.012] Allocated cache and file handles         database=/tmp/BenchmarkFilters2692416678/001 cache=16.00MiB handles=16
INFO [11-09|08:46:50.013] Persisted trie from memory database      nodes=1 size=142.00B time="5.393µs" gcnodes=0 gcsize=0.00B gctime=0s livenodes=1 livesize=0.00B
INFO [11-09|08:46:53.099] Persisted trie from memory database      nodes=1 size=142.00B time="116.421µs" gcnodes=0 gcsize=0.00B gctime=0s livenodes=1 livesize=0.00B
goos: linux
goarch: amd64
pkg: github.com/ethereum/go-ethereum/eth/filters
cpu: Intel(R) Core(TM) i9-10885H CPU @ 2.40GHz
BenchmarkFilters-8             1        1398357927 ns/op
PASS
ok      github.com/ethereum/go-ethereum/eth/filters     6.783s