Add info to PF6 migration guide regarding potential test suite impacts

[wise-king-sullyman]

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Is this a new page or a change to an existing one? Addition to the existing migration guide

Describe the enhancement We should add some documentation explaining likely test failures resulting from:

1. the addition of a wrapper div to Button
2. the change to the behavior of aria-disabled on Button when using the isDisabled prop
3. potential issues with Popper content being aria-disabled in jest in some cases

Related to issues: https://github.com/patternfly/patternfly-react/issues/10926 https://github.com/patternfly/patternfly-react/issues/10927 https://github.com/patternfly/patternfly-react/issues/10928