fix: when company is created with other company template Chart of Account the Create Taxe Template failed (backport #42755)

[mergify]

Please provide enough information so that others can review your pull request:

On setup create "Company 1" in country Germany with charts of account template : SKR04 ohne Kontonummern
Use feature button Create Tax Template => OK
Create another company use template chart of account from "Company 1"
Use feature button Create Tax Template => KO

Explain the details for making this change. What existing problem does the pull request solve?

If field create_chart_of_accounts_based_on is set on a company use existing_company to find correct chart of account

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This is an automatic backport of pull request #42755 done by Mergify.