[JENKINS-72364] Close provider dialog window when cancel is clicked

One change from #491
was applied to a reference that was not using Prototype.js.

https://issues.jenkins.io/browse/JENKINS-72364 is the issue report.

Confirmed interactively that I can see the problem before the change
and that with this change the problem is resolved.

src/main/resources/lib/credentials/dialog.js

@@ -3,5 +3,5 @@ Behaviour.specify("#credentials-add-submit", 'credentials-dialog-add', 0, functi
 });
 
 Behaviour.specify("#credentials-add-abort", 'credentials-dialog-abort', 0, function (e) {
-    e.onclick = (_) => window.credentials.dialog.style.display = "none";
+    e.onclick = (_) => window.credentials.dialog.hide();
 });