Avoid importing internal_transactions of pending transactions

[pasqu4le]

Solves:

application=indexer fetcher=internal_transaction step=internal_transactions_indexed_at_transactions
count=10 error_count=10 [error] failed to import internal transactions for transactions:
%{exception: %Postgrex.Error{connection_id: 25257, message: nil, postgres: %{code:
:check_violation, constraint: "status", detail: "Failing row contains (null, null, 
[...]

Motivation

The problem happens because while fetching internal transactions for a block sometimes we receive some that are part of a pending transaction (or at least a transaction that is still registered in the database as pending).
By inserting them we also try to update the pending transaction's field, but this violates the status check constraint (and rightfully so).

Changelog

Bug Fixes

The solution is to filter out internal_transactions that are part of a pending transaction before trying to insert them.

Checklist for your PR

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so if necessary
• If I added/changed/removed ENV var, I should update the list of env vars in https://github.com/poanetwork/blockscout/blob/master/docs/env-variables.md to reflect changes in the table here https://poanetwork.github.io/blockscout/#/env-variables?id=blockscout-env-variables
• If I add new indices into DB, I checked, that they don't redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build 054780bf-8506-4ac2-b34e-4264de6ea16c

• 7 of 7 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 79.307%

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Totals
Change from base Build 5bb5bf01-fa26-4c36-9e25-d26613662757:	0.02%
Covered Lines:	5170
Relevant Lines:	6519

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💛 - Coveralls