Resolve "All get next buttons show even if lab is closed"

What does this mr do?

all the get next buttons show, even if the actual lab is not open.

Actions taken to fix bug

add an if statement to only show the button if the lab is open.

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made and the bug I fixed.
• A test was created to test the bug.
• I have updated the documentation accordingly.
• I adhere to the style guide.

Closes #332 (closed)

src/main/resources/templates/request/list.html

@@ -50,7 +50,7 @@
             <div class="float-right btn-toolbar">
                 <form th:each="lab : ${activeLabs}" th:action="@{'/requests/next/' + ${lab.id}}"
                       class="float-right" style="padding-right:2px;" method="POST">
-                    <button type="submit" class="btn btn-sm btn-primary"
+                    <button type="submit" class="btn btn-sm btn-primary" th:if="${lab.isOpen()}"
                             th:classappend="${queued.get(lab.id) == 0} ? disabled : ''">Get next for
                         [[${lab.course.code}]] [[${lab.toString()}]] (<span th:id="${'span-' + lab.id}">[[${queued.get(lab.id)}]]</span>)
                     </button>