patch 8.2.0183: tests fail when the float feature is disabled

Problem:    Tests fail when the float feature is disabled.
Solution:   Skip tests that don't work without float support.
diff --git a/src/testdir/test_user_func.vim b/src/testdir/test_user_func.vim
index 4b4a276..d10a110 100644
--- a/src/testdir/test_user_func.vim
+++ b/src/testdir/test_user_func.vim
@@ -121,9 +121,11 @@
 endfunc
 
 func Test_default_arg()
-  call assert_equal(1.0, Log(10))
-  call assert_equal(log(10), Log(10, exp(1)))
-  call assert_fails("call Log(1,2,3)", 'E118')
+  if has('float')
+    call assert_equal(1.0, Log(10))
+    call assert_equal(log(10), Log(10, exp(1)))
+    call assert_fails("call Log(1,2,3)", 'E118')
+  endif
 
   let res = Args(1)
   call assert_equal(res.mandatory, 1)