patch 9.0.0564: a few tests keep failing on MacOS M1

Problem:    A few tests keep failing on MacOS M1.
Solution:   Add a test check CheckNotMacM1.  Fix timer tests.
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index 3c95f87..86732f1 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -2998,6 +2998,8 @@
 " Tests for SigUSR1 autocmd event, which is only available on posix systems.
 func Test_autocmd_sigusr1()
   CheckUnix
+  " FIXME: should this work on MacOS M1?
+  CheckNotMacM1
   CheckExecutable /bin/kill
 
   let g:sigusr1_passed = 0