u02/tests: Use floats for r/d in circle prop test

It does not improve the test’s accuracy, but it seems weird to first
convert the radius to an int and then save the distance as a double.

u02/src/tests.cpp

@@ -352,7 +352,7 @@ TEST_CASE("Bresenham circle (prop: √(x²+y²)-r<ε)") {
     SKIP("All coordinates have extreme value, skipping (avoid rounding error)");
   }
 
-  const int r =
+  const float r =
       round(std::sqrt(std::pow((x1 - x0), 2) + std::pow((y1 - y0), 2)));
 
   canvas_buffer *canvas = new canvas_buffer(size, size);
@@ -363,7 +363,7 @@ TEST_CASE("Bresenham circle (prop: √(x²+y²)-r<ε)") {
   bool pass = true;
   for (int x = 0; x < size; x++) {
     for (int y = 0; y < size; y++) {
-      double distance =
+      float distance =
           std::abs(std::sqrt(std::pow(x0 - x, 2) + std::pow(y0 - y, 2)) - r);
       // Because of rounding errors, an exact test (for all pixels) is not
       // feasible.