BUG: fix default string dtype used for pandas 3 #797

Job	Run time
${{ matrix.os }} ${{ matrix.architecture }} ${{ matrix.linux_archs }}	0s
${{ matrix.os }} ${{ matrix.architecture }} ${{ matrix.linux_archs }}	0s
${{ matrix.os }} ${{ matrix.architecture }}	0s
${{ matrix.os }} ${{ matrix.architecture }}	0s
${{ matrix.os }} ${{ matrix.architecture }}	0s
	0s

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