Fix tx deserialisation for adding nonce

[angrybayblade]

Proposed changes

Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request.

Fixes

fixes #704

Types of changes

What types of changes does your code introduce to agents-aea? Put an x in the boxes that apply

• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply.

• [ ] I have read the CONTRIBUTING doc
• [ ] I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• [ ] Lint and unit tests pass locally with my changes and CI passes too
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have checked that code coverage does not decrease.
• [ ] I have added necessary documentation (if appropriate)
• [ ] Any dependent changes have been merged and published in downstream modules

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (9734de0) 90.24% compared to head (b672822) 90.26%.

Files	Patch %	Lines
...gins/aea-ledger-solana/aea_ledger_solana/solana.py	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #707 +/- ## ========================================== + Coverage 90.24% 90.26% +0.01% ========================================== Files 371 371 Lines 29815 29814 -1 ========================================== + Hits 26906 26911 +5 + Misses 2909 2903 -6 ``` | [Flag](https://app.codecov.io/gh/valory-xyz/open-aea/pull/707/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=valory-xyz) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/valory-xyz/open-aea/pull/707/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=valory-xyz) | `90.26% <85.71%> (+0.01%)` | :arrow_up: | 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=valory-xyz#carryforward-flags-in-the-pull-request-comment) to find out more.

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