fix(deps): update dependency org.jfree:jfreechart to v1.5.6

[renovate-bot]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
org.jfree:jfreechart (source)	1.5.5 -> 1.5.6

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Release Notes

jfree/jfreechart (org.jfree:jfreechart)

v1.5.6: JFreeChart 1.5.6

Version 1.5.6 (21 May 2025)

• added setSymbols method to SymbolAxis (#​421)
• added label padding to Crosshair (#​414)
• add clearSeriesXXX methods for all series settings in AbstractRenderer (#​364)
• fix calculating if label fits inside bar for XYBarRenderer (#​366)
• set default background paint to LIGHT_GRAY (#​324)
• deprecated all classes in org.jfree.chart.servlet.* (#​385)
• updated pom.xml with new Maven publishing flow and latest plugin versions
• various minor improvements

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