Vaadin 25: HeaderFooterStylesIT integration tests fail #158

Describe the bug

testHeaderClassesApplied: org.junit.ComparisonFailure: expected:<[]row0-cell0> but was:<[cell header-cell first-column-cell first-header-row-cell ]row0-cell0>
testHeaderCellMutability: org.junit.ComparisonFailure: expected:<[]row0-cell1> but was:<[cell header-cell first-header-row-cell first-column-cell ]row0-cell1>

Expected behavior

Integration tests must pass.

Minimal reproducible example

No response

Add-on Version

2.0.0-SNAPSHOT

Vaadin Version

25.0.0

Additional information

This is likely caused by the changes in #153