curl: --test-duphandle in debug builds runs "duphandled"

Using this option (only available in debug builds) makes curl always
call curl_easy_duphandle() on the handle before using it.

To help us catch curl_easy_duphandle() mistakes better.

Add a CI job using this.

Bonus: the previous runtests option -e is now also supported as
--test-event

Closes #15504

tests/data/test441

@@ -44,6 +44,9 @@ HSTS with no t-dot host name in URL but t-dot in file
 <command>
 -x http://%HOSTIP:%HTTPPORT http://this.hsts.example/%TESTNUMBER --hsts %LOGDIR/input%TESTNUMBER -w '%{url_effective}\n'
 </command>
+<disable>
+test-duphandle
+</disable>
 </client>
 
 <verify>