fix(test): exclude lock file from storage files count

[keroro520]

The static_file tests assert the count of storage files. However, when the feature flag "reth-db/disable-lock" is enabled, the lock file is not created. This inconsistency affects the file count assertions in tests.

This PR modifies the storage files counting logic to exclude the lock file, ensuring consistent test behavior regardless of whether the "disable-lock" feature is enabled or not.

---

Reproduce the failed tests:

cargo nextest run -v --locked --workspace --features 'jemalloc-prof' -E 'kind(lib)' -E 'kind(bin)' -E 'kind(proc-macro)' test_tx_based_truncation test_header_truncation

# or simply
make test-unit

Part of the output:

--- TRY 3 STDERR:        reth-provider providers::static_file::tests::test_tx_based_truncation ---
thread 'providers::static_file::tests::test_tx_based_truncation' panicked at crates/storage/provider/src/providers/static_file/mod.rs:548:18:
called `Result::unwrap()` on an `Err` value: Test case 0: file count mismatch | got: 9 expected: 10)

Location:
    crates/storage/provider/src/providers/static_file/mod.rs:547:32
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[mattsse]

removing the +1 is a lot nicer.

makes sense

pending @joshieDo

[keroro520]

@mattsse @joshieDo e7db8e5 makes some fixes. PTAL