silx.gui.plot.iterms: Fixed Marker.setSymbolSize #1707

Job	Run time
Python 3.8 on ubuntu-20.04 PyQt5	10m 7s
Python 3.11 on ubuntu-latest PyQt6	8m 58s
Python 3.12 on ubuntu-latest PySide6	7m 5s
Python 3.10 on macos-13 PyQt5	15m 49s
Python 3.12 on macos-13 PyQt6	19m 32s
Python 3.9 on macos-13 PySide6	8m 49s
Python 3.9 on windows-latest PyQt5	8m 54s
Python 3.12 on windows-latest PyQt6	9m 58s
Python 3.10 on windows-latest PySide6	8m 41s
	1h 37m 53s

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