speakup-dummy: Add support for PUNCT variable

This allows to debug the update of the punctuation level.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

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Link: https://lore.kernel.org/r/20220823222514.929670068@ens-lyon.org

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>