🪲 [Fix]: Package test dependency uses an invalid Pester 6 upper bound

[MariusStorhaug]

Problem

Publishing the module cannot serialize the test requirement's Pester maximum version 6.* into NuGet package metadata.

Expected outcome

The packaged test dependency resolves to the concrete NuGet constraint [6.0.0, 6.999.999], retaining support for all Pester 6 releases without blocking package publication.

Scope

Update only the test requirement version bound and validate the focused Pester suite.