patch 9.0.0323: using common name in tests leads to flaky tests

Problem:    Using common name in tests leads to flaky tests.
Solution:   Rename files and directories to be more specific.
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index 0f6a501..c398bb0 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -630,12 +630,12 @@
     CheckExecutable pwd
     let cmd = 'pwd'
   endif
-  call mkdir('Xdir')
-  let buf = term_start(cmd, {'cwd': 'Xdir'})
-  call WaitForAssert({-> assert_equal('Xdir', fnamemodify(getline(1), ":t"))})
+  call mkdir('Xtermdir')
+  let buf = term_start(cmd, {'cwd': 'Xtermdir'})
+  call WaitForAssert({-> assert_equal('Xtermdir', fnamemodify(getline(1), ":t"))})
 
   exe buf . 'bwipe'
-  call delete('Xdir', 'rf')
+  call delete('Xtermdir', 'rf')
 endfunc
 
 func Test_terminal_cwd_failure()