[Bug] Tests cannot be run with a central funding account as described in the README

## Bug description
Tests cannot be run as described when funding new accounts with a central funding address as described in [`identity_iota_core` README](https://github.com/iotaledger/identity/blob/main/identity_iota_core/README.md?plain=1#L16).

New accounts receive 0.5 IOTA, while an internal check aborts due to them not having enough funds (1 IOTA).

This only affects runs with a central funding account, regular test runs are not affected.

## Language version
What programming language are you using? Rust or one of the bindings?
Which version of the language are you running?

- Language: Rust
- Version: rustc 1.91.1 (ed61e7d7e 2025-11-07)

## IOTA Identity version
Which version of IOTA Identity are you using?

- Version (version number, commit, or branch): current main branch (1.8.0-beta.3), rev c6e2f2a2ac4ae1d4ccfec63fd05a34722585e097

## Steps To reproduce the bug
Explain how the maintainer can reproduce the bug.

1. have an address with enough funds as active address
2. run `IOTA_IDENTITY_FUND_WITH_ACTIVE_ADDRESS=true cargo test -- --test-threads=1` (or limit it to a specific test, that does on-chain interaction)

## Expected behaviour
Tests complete successfully.

## Actual behaviour
Test(s) fail with an error, that new test account does not have enough funds.

## Errors
> Error: issue with gas for transaction: issue with gas for transaction: no coin found with minimum required balance of 1000000000 for address 0x07f654ac8afe131cfebe8ff0b094591def1b26fa690d769ee98e59270b9caebf