fix: Sticky header scrolls away in FluentDataGrid

[bLinMil]

🐛 Bug Report

I have a header that I want to add borders on the th cells to distinguish them from each other. When I do that, they appear.
However, when I scroll my data grid, the borders scroll away.

💻 Repro or Code Sample

@page "/test"

<style>
    .column-header {
        border-right: 2px solid;
    }
</style>

<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<div style="height: 200px;">
    <FluentDataGrid DisplayMode="DataGridDisplayMode.Table" TGridItem="Testt" Items="testList.AsQueryable()" GenerateHeader="GenerateHeaderOption.Sticky">
        <TemplateColumn Sortable="true" Title="First Column Header" Align="Align.Center" Width="200px">
            @context.a
        </TemplateColumn>
        <TemplateColumn Sortable="true" Title="Second Column Header" Align="Align.Center" Width="200px">
            @context.b
        </TemplateColumn>
        <TemplateColumn Sortable="true" Title="Third Column Header" Align="Align.Center" Width="200px">
            @context.c
        </TemplateColumn>
    </FluentDataGrid>
</div>


@code {
    class Testt
    {
        public string a = "a";
        public string b = "b";
        public string c = "c";
    }

    private List<Testt> testList = new()
    {
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
        new(),
    };
}

Before scrolling

After scrolling

The th's are fixed but the tr scrolls away for the header

🤔 Expected Behavior

When I scroll, I want to the header to stay sticky but I also want the .column-header classes to have the borders and for them to stay put.

😯 Current Behavior

The borders scroll away when I scroll the table

🔦 Context

In a more complex table, I have a column options button and so the borders help distinguish which option button applies to each header.

🌍 Your Environment

Windows
Edge
Fluent 4.11.2 dotnet 8.0.404