Bug 1593622 - Test console autocompletion after ?? (nullish coalescing operator). r=Honza.

The nullish coalescing operator was added last week in Spidermonkey.
It looks like there isn't anything to do to support it on the console
side, so we only add a test for the autocompletion after it, to make
sure we don't regress this in the future.

Differential Revision: https://phabricator.services.mozilla.com/D51632

--HG--
extra : moz-landing-system : lando

devtools/shared/webconsole/test/test_jsterm_autocomplete.html

@@ -508,6 +508,7 @@
       "x=true?foob",
       "x=false?1:foob",
       "!foob",
+      "false??foob",
     ];
 
     for (const input of inputs) {