patch 8.1.1774: test is silently skipped

Problem:    Test is silently skipped.
Solution:   Throw "Skipped".

src/testdir/test_ins_complete.vim

@@ -335,7 +335,7 @@ endfunc
 " Test for insert path completion with completeslash option
 func Test_ins_completeslash()
   if !has('win32')
-    return
+    throw 'Skipped: only works on MS-Windows'
   endif
   
   call mkdir('Xdir')

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1774,
 /**/
     1773,
 /**/