patch 9.0.0428: autocmd test uses common file name

Problem:    Autocmd test uses common file name.
Solution:   Use unique name to reduce flakiness.
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index 458ac38..17bfd1b 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -756,7 +756,7 @@
     augroup END
 
     func WriteErrors()
-      call writefile([execute("messages")], "Xerrors")
+      call writefile([execute("messages")], "XerrorsBwipe")
     endfunc
     au VimLeave * call WriteErrors()
   [CODE]
@@ -764,11 +764,11 @@
   call writefile(content, 'Xvimrc', 'D')
   call system(GetVimCommand('Xvimrc') .. ' --not-a-term --noplugins -S Session.vim -c cq')
   sleep 100m
-  let errors = join(readfile('Xerrors'))
+  let errors = join(readfile('XerrorsBwipe'))
   call assert_match('E814:', errors)
 
   set swapfile
-  for file in ['Session.vim', 'Xerrors']
+  for file in ['Session.vim', 'XerrorsBwipe']
     call delete(file)
   endfor
 endfunc
@@ -781,16 +781,16 @@
       edit foo1
       au BufNew,BufAdd,BufWinEnter,BufEnter,BufLeave,BufWinLeave,BufUnload,VimEnter foo* ball
       edit foo2
-      call writefile(['OK'], 'Xerrors')
+      call writefile(['OK'], 'XerrorsBlast')
       qall
   [CODE]
 
   call writefile(content, 'XblastBall', 'D')
   call system(GetVimCommand() .. ' --clean -S XblastBall')
   sleep 100m
-  call assert_match('OK', readfile('Xerrors')->join())
+  call assert_match('OK', readfile('XerrorsBlast')->join())
 
-  call delete('Xerrors')
+  call delete('XerrorsBlast')
 endfunc
 
 " SEGV occurs in older versions.
@@ -817,7 +817,7 @@
     au SessionLoadPost * call DeleteInactiveBufs()
 
     func WriteErrors()
-      call writefile([execute("messages")], "Xerrors")
+      call writefile([execute("messages")], "XerrorsPost")
     endfunc
     au VimLeave * call WriteErrors()
   [CODE]
@@ -825,13 +825,13 @@
   call writefile(content, 'Xvimrc', 'D')
   call system(GetVimCommand('Xvimrc') .. ' --not-a-term --noplugins -S Session.vim -c cq')
   sleep 100m
-  let errors = join(readfile('Xerrors'))
+  let errors = join(readfile('XerrorsPost'))
   " This probably only ever matches on unix.
   call assert_notmatch('Caught deadly signal SEGV', errors)
   call assert_match('SessionLoadPost DONE', errors)
 
   set swapfile
-  for file in ['Session.vim', 'Xerrors']
+  for file in ['Session.vim', 'XerrorsPost']
     call delete(file)
   endfor
 endfunc