Fix pricing

[Adamantios]

Proposed changes

Fixes the pricing logic.

Fixes

Closes #735.

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

Further comments

n/a

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.09%. Comparing base (9d887d6) to head (7eb0ad9).
Report is 73 commits behind head on main.

Files with missing lines	Patch %	Lines
...ea-ledger-ethereum/aea_ledger_ethereum/ethereum.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #756      +/-   ##
==========================================
- Coverage   90.21%   90.09%   -0.13%     
==========================================
  Files         373      331      -42     
  Lines       29899    29567     -332     
==========================================
- Hits        26974    26638     -336     
- Misses       2925     2929       +4     

Flag	Coverage Δ
unittests	90.09% <90.90%> (-0.13%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.