patch 8.1.1193: typos and small problems in test files

Problem:    Typos and small problems in test files.
Solution:   Small improvements.
diff --git a/src/testdir/test_quotestar.vim b/src/testdir/test_quotestar.vim
index ce5a9ee..c7e38ae 100644
--- a/src/testdir/test_quotestar.vim
+++ b/src/testdir/test_quotestar.vim
@@ -97,7 +97,7 @@
   if has('unix') && has('gui') && !has('gui_running')
     let @* = ''
 
-    " Running in a terminal and the GUI is avaiable: Tell the server to open
+    " Running in a terminal and the GUI is available: Tell the server to open
     " the GUI and check that the remote command still works.
     " Need to wait for the GUI to start up, otherwise the send hangs in trying
     " to send to the terminal window.