patch 8.2.0373: type of term_sendkeys() is unknown

Problem:    Type of term_sendkeys() is unknown.
Solution:   Just return zero. (closes #5762)
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index 7bdabb8..8d32cbc 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -368,7 +368,11 @@
   call term_wait(buf)
   call term_sendkeys(buf, "exit\<CR>")
   call term_wait(buf)
-  call term_sendkeys(buf, ":q\<CR>")
+  let tsk_ret = term_sendkeys(buf, ":q\<CR>")
+
+  " check type of term_sendkeys() return value
+  echo type(tsk_ret)
+
   call StopVimInTerminal(buf)
   call delete('XTest_postponed')
   call delete('Xtext')