fix: Fix dtype of array returned by canny_edge_detection

[Czaki]

The CannyEdgeDetection returns the same dtype as the input image, where plugin_function converts data to floats.

So it is required to convert data to some integer type to be valid lable dtype.

[haesleinhuepf]

git-bob review

[github-actions]

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The pull request addresses the issue of the dtype of the array returned by canny_edge_detection. The change applies a casting to sitkUInt8, ensuring that the output is a valid label dtype, as discussed. This change is minimal and directly resolves the issue described in the pull request. The code modification aligns with the requirement to convert the output to an integer type, consistent with the discussion. Everything looks good.

[haesleinhuepf]

Awesome, thanks @Czaki !