patch 8.2.4611: typos in tests; one lua line not covered by test

Problem:    Typos in tests; one lua line not covered by test.
Solution:   Fix typos. Add test case. (Dominique Pellé, closes #9994)
diff --git a/src/testdir/test_signals.vim b/src/testdir/test_signals.vim
index d3a4d89..2cf0dd7 100644
--- a/src/testdir/test_signals.vim
+++ b/src/testdir/test_signals.vim
@@ -99,8 +99,8 @@
   call term_sendkeys(buf, ":while 1 | endwhile\n")
   call WaitForAssert({-> assert_equal(':while 1 | endwhile', term_getline(buf, 6))})
   exe 'silent !kill -s INT ' .. pid_vim
-  call term_sendkeys(buf, ":call setline(1, 'INTERUPTED')\n")
-  call WaitForAssert({-> assert_equal('INTERUPTED', term_getline(buf, 1))})
+  call term_sendkeys(buf, ":call setline(1, 'INTERRUPTED')\n")
+  call WaitForAssert({-> assert_equal('INTERRUPTED', term_getline(buf, 1))})
 
   call StopVimInTerminal(buf)
 endfunc