patch 9.0.0363: common names in test files causes tests to be flaky

Problem:    Common names in test files causes tests to be flaky.
Solution:   Use more specific names.
diff --git a/src/testdir/test_indent.vim b/src/testdir/test_indent.vim
index 3b5b643..97c44b8 100644
--- a/src/testdir/test_indent.vim
+++ b/src/testdir/test_indent.vim
@@ -161,9 +161,9 @@
   func GetIndent()
     return line('.') * 2
   endfunc
-  call writefile(['# vim: indentexpr=GetIndent()'], 'Xfile.txt')
+  call writefile(['# vim: indentexpr=GetIndent()'], 'Xmlfile.txt')
   set modelineexpr
-  new Xfile.txt
+  new Xmlfile.txt
   call assert_equal('GetIndent()', &indentexpr)
   exe "normal Oa\nb\n"
   call assert_equal(['  a', '    b'], getline(1, 2))
@@ -172,7 +172,7 @@
   delfunc GetIndent
   let &modeline = modeline
   close!
-  call delete('Xfile.txt')
+  call delete('Xmlfile.txt')
 endfunc
 
 func Test_indent_func_with_gq()