Update dependency payrexx/payrexx to v1.8.8

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
payrexx/payrexx (source)	1.8.5 -> 1.8.8

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Release Notes

payrexx/payrexx-php (payrexx/payrexx)

v1.8.8

Compare Source

• Changed Payout Amount Data Type To Int

v1.8.7

Compare Source

• Added Create Manual Payout Functionality
• Added Field HeaderCustomLink to Design-Entity
• Added Information About Specifying a Custom Base Domain

v1.8.6

Compare Source

• Changed composer.json to require at least PHP 7.4
• Added new fee attribute to transaction class
• Added PHPStan to check types and other circumstances and warns about errors

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