`TextElement.tspans()` should retrieve all the tspans recursively
https://gitlab.com/inkscape/extensions/-/blob/master/inkex/elements/_text.py#L121
Nested tspans are not retrieved, so if text is in the nested tspans, get_text()
doesn't return the correct string.
Proposed solution:
def tspans(self):
"""Returns all children that are tspan elements"""
return self.findall(".//svg:tspan")