patch 8.1.0459: Test_executable fails when there is a dog in the system

Problem:    Test_executable fails when there is a dog in the system.
Solution:   Rename the dog. (Hirohito Higashi)
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index d601c27..e59cdf8 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -855,7 +855,7 @@
     call assert_equal(0, executable('win.ini'))
   elseif has('unix')
     call assert_equal(1, executable('cat'))
-    call assert_equal(0, executable('dog'))
+    call assert_equal(0, executable('nodogshere'))
   endif
 endfunc