Update dependency ufo2ft to v3.9.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
ufo2ft	==3.8.2 → ==3.9.0

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Release Notes

googlefonts/ufo2ft (ufo2ft)

v3.9.0

Compare Source

• [outlineCompiler] Building the glyf table is now O(n) instead of O(n²) independent of the installed fontTools version (#​991).
• [filters] Added an explicitClosingLine filter to fix interpolatable CFF masters producing mismatched Type 2 charstrings when a contour's end point coincides with its start point (fonttools/fonttools#4114, #​993).
• [kernFeatureWriter] Fixed the variable-features kern writer (variableFeatures=True) emitting incorrect kerning values when kern group membership diverges across masters. Each pair is now resolved against each source's own groups, and classes whose membership diverges are refined into the coarsest common refinement (the same partition varLib.merge derives), so a family switching from varLib merging to single variable features no longer has its kerning silently mis-compiled. The same fix also applies to the legacy kernFeatureWriter2 (#​992, #​996).
• [kernFeatureWriter] Fixed the variable-features kern writer hollowing kerning toward 0 across full (non-layer) UFO masters that carry no kerning at all (e.g. Roboto Flex's parametric-axis masters). Such kernless non-default sources are now skipped when building the kern VariableScalars, mirroring the varLib.merger path's exclusion of masters that compile to no GPOS table; the default source is always kept (#​995, #​997).

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