patch 8.0.0156: not enough test coverage for float functions

Problem:    Several float functions are not covered by tests.
Solution:   Add float tests. (Dominique Pelle)

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    156,
 /**/
     155,
 /**/