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/test440

@@ -44,6 +44,10 @@ HSTS with trailing-dot host name in URL but none in hsts 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>

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>

tests/data/test493

@@ -43,6 +43,9 @@ HSTS and %{url_effective} after upgrade
 <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>

tests/data/test780

@@ -55,6 +55,9 @@ HSTS with updated expiry in response
 <command>
 -x http://%HOSTIP:%PROXYPORT http://this.hsts.example:%HTTPSPORT/%TESTNUMBER --hsts %LOGDIR/input%TESTNUMBER -k
 </command>
+<disable>
+test-duphandle
+</disable>
 </client>
 
 <verify>

tests/data/test781

@@ -57,6 +57,9 @@ HSTS update expiry, with parent includeSubDomains domain present
 <command>
 -x http://%HOSTIP:%PROXYPORT http://this.hsts.example:%HTTPSPORT/%TESTNUMBER --hsts %LOGDIR/input%TESTNUMBER -k
 </command>
+<disable>
+test-duphandle
+</disable>
 </client>
 
 <verify>

tests/data/test782

@@ -57,6 +57,9 @@ HSTS update expiry, with two includeSubDomains domains present
 <command>
 -x http://%HOSTIP:%PROXYPORT http://this.hsts.example:%HTTPSPORT/%TESTNUMBER --hsts %LOGDIR/input%TESTNUMBER -k
 </command>
+<disable>
+test-duphandle
+</disable>
 </client>
 
 <verify>

tests/data/test783

@@ -57,6 +57,9 @@ HSTS update expiry, removing includesubdomains in update
 <command>
 -x http://%HOSTIP:%PROXYPORT http://this.hsts.example:%HTTPSPORT/%TESTNUMBER --hsts %LOGDIR/input%TESTNUMBER -k
 </command>
+<disable>
+test-duphandle
+</disable>
 </client>
 
 <verify>