Minor HTML edit on my_checks.html

I wanted to check the cron cheatsheet and got annoyed because it opened on the same tab, so I had to go back and open the window/modal to edit the cron period, and open the cheatsheet again, but this time on a new tab, so I could build my cron expression side-by-side.

templates/front/my_checks.html

@@ -197,7 +197,7 @@
                                     placeholder="* * * * *">
                                 <div id="schedule-hint">
                                     m h dom mon dow
-                                    <a href="{% url 'hc-docs-cron' %}">(cheatsheet)</a>
+                                    <a href="{% url 'hc-docs-cron' %}" target="_blank">(cheatsheet)</a>
                                 </div>
                             </div>
                         </div>