[srgpqt]

Tiny fix for the pixel ratio calculation in the nanovg example.

The previous f32(fw) / f32(fw) would obviously always produce an incorrect pixel ratio 1.

• This example has been added to .github/workflows/check.yml (for automatic testing)
• This example compiles cleanly with flags -vet -strict-style -vet-tabs -disallow-do -warnings-as-errors
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