Comments in ColumnGroup rows are rendered as <th> elements

[ltlBeBoy]

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[X ] bug report
[ ] feature request
[ ] support request

Current behavior
primevue/src/components/datatable/TableHeader.vue renders comments in ColumnGroup rows as th. This is because there is a loop over the row children which does not check whether the child is a Column or not.

Expected behavior
Comments are ignored when rendering.

Minimal reproduction of the problem with instructions
The following example will render seven instead of five columns:

    <ColumnGroup type="header">
      <Row>
        <Column header="A" :rowspan="2" />
        <Column header="B" :colspan="2" />
        <Column header="C" :colspan="2" />
      </Row>
      <Row>
        <!-- Comment B -->
        <Column header="B1" />
        <Column header="B2" />

        <!-- Comment C -->
        <Column header="C1" />
        <Column header="C1" />
      </Row>
    </ColumnGroup>

What is the motivation / use case for changing the behavior?
Bugfix.

Please tell us about your environment:
Debian Linux 9; Visual Studio Code 1.57.1; Firefox 78.11.0esr (64-Bit)

• Vue version: 3.1.2

• PrimeVue version: 3.5.1

• Browser: all