Don't check for :safe-renegotiation with TLS1.3

* lisp/net/nsm.el (nsm-protocol-check--renegotiation-info-ext): Don't
check when using TLS1.3, renegotiation has been removed from TLS.
Reported in
<https://lists.gnu.org/archive/html/help-gnu-emacs/2019-09/msg00005.html>
1 job for master in 58 minutes and 12 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #3204
test-all

00:58:12

 
Name Stage Failure
failed
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:319: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:294: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1