fix: reliable commit tx in unit tests

[codecov-commenter]

Codecov Report

Base: 77.08% // Head: 77.06% // Decreases project coverage by -0.01% :warning:

Coverage data is based on head (afbdc1c) compared to base (9a42b4c). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #88 +/- ## =========================================== - Coverage 77.08% 77.06% -0.02% =========================================== Files 23 23 Lines 4504 4505 +1 =========================================== Hits 3472 3472 - Misses 1032 1033 +1 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `77.06% <ø> (-0.02%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nervosnetwork#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/nervosnetwork/ckb-light-client/pull/88?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nervosnetwork) | Coverage Δ | | |---|---|---| | [src/types.rs](https://codecov.io/gh/nervosnetwork/ckb-light-client/pull/88/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nervosnetwork#diff-c3JjL3R5cGVzLnJz) | `0.00% <0.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nervosnetwork). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nervosnetwork)

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