s2cell_test: Increase TestCellDistanceToEdge tolerance

This has already been done in C++.

https://github.com/google/s2geometry/blob/58de4ea1e2f8a294e0c072c602c22232fd1433ad/src/s2/s2cell_test.cc#L656

Author: jmr

s2/cell_test.go

@@ -666,8 +666,8 @@ func TestCellDistanceToEdge(t *testing.T) {
 		// Pi for vertex distance.
 		expectedError := 1e-12
 		if expectedMin.Radians() > math.Pi/2 {
-			// Max error for ChordAngle as it approaches Pi is about 2e-8.
-			expectedError = 2e-8
+			// Max error for ChordAngle as it approaches Pi is about 3e-8.
+			expectedError = 3e-8
 		} else if expectedMin.Radians() <= math.Pi/3 {
 			expectedError = 1e-15
 		}