patch 8.2.1432: various inconsistencies in test files

Problem:    Various inconsistencies in test files.
Solution:   Add modelines where they were missing.  Use Check commands instead
            of silently skipping over tests.  Adjust indents and comments.
            (Ken Takata, closes #6695)

src/testdir/test_nested_function.vim

@@ -1,5 +1,7 @@
-"Tests for nested functions
-"
+" Tests for nested functions
+
+source check.vim
+
 func NestedFunc()
   func! Func1()
     let g:text .= 'Func1 '
@@ -49,9 +51,8 @@ endfunc
 
 func Test_max_nesting()
   " TODO: why does this fail on Windows?  Runs out of stack perhaps?
-  if has('win32')
-    return
-  endif
+  CheckNotMSWindows
+
   let call_depth_here = 2
   let ex_depth_here = 5
   set mfd&
@@ -65,3 +66,5 @@ func Test_max_nesting()
 
   set mfd&
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab