tests: Increase timeouts instead of disabling them (#10367)

Some tests were disabled in ba799c67f9 and
10567d81e2, because they tend to
frequently time out after 8 seconds.

Instead of disabling the tests (which IMHO is bad, because tests are
there for a reason), we're now increasing the timeout to 30 seconds just
for these tests.

As requested by @paglias, I've marked the timeout functions with a @TODO
comment, so that the slow tests or the functionality they're testing are
eventually refactored.

I also needed to change the arrow notation for the test cases to use the
function keyword, because otherwise we don't have this.timeout()
available.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @paglias

test/api/v3/integration/challenges/GET-challenges_challengeId_members.test.js

@@ -123,8 +123,8 @@ describe('GET /challenges/:challengeId/members', () => {
     });
   });
 
-  // @TODO times out too many times (when it takes more than 8s)
-  xit('supports using req.query.lastId to get more members', async () => {
+  it('supports using req.query.lastId to get more members', async function () {
+    this.timeout(30000); // @TODO: times out after 8 seconds
     let group = await generateGroup(user, {type: 'party', name: generateUUID()});
     let challenge = await generateChallenge(user, group);