The unit tests for web-sveltekit have become flaky, and have therefore
been set to run only manually:
https://github.com/sourcegraph/sourcegraph/pull/63874

By running them via `sg ci bazel` I noticed in the waterfall view, that
the tests are taking slightly above one minute
(https://buildkite.com/sourcegraph/sourcegraph/builds/282732/waterfall),
and that previous tests failed because it exceeded a timeout of 1
minute: https://buildkite.com/sourcegraph/sourcegraph/builds/282684

It looks to me like the CI agents are a bit less powerful, and therefore
take longer than our local test runs (which usually don't exceed 10
seconds).

I have not investigated parallelizing the vitest workers, because for
web-sveltekit we currently only have a vite config, but not a vitest
config. More context on that here:
https://github.com/sourcegraph/sourcegraph/pull/60927

## Test plan

CI

## Changelog

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The goal of this PR is to increase the stability of web-sveltekit
e2e-tests so that we don't have to rely on manual runs anymore. They
have previously been disabled due to a high number of failures:
https://github.com/sourcegraph/sourcegraph/pull/63874

---

To improve the stability of web-sveltekit e2e-tests, I used `sg ci bazel
test //client/web-sveltekit:e2e_test --runs_per_test=N` with N=5,10,15
to see which tests break under different levels of pressure on the
machine. The logs looked like it was mostly timeouts, that got worse
when increasing N. That means we can check where tests will break due to
timeouts, but we don't really need to raise timeouts so far that it
would work with N=20.

With N=5, 10 we get a good understanding if our timeouts are high
enough.

You can see two CI runs here after applying higher timeouts and skipping
a consistently failing test:

- N=5:
https://buildkite.com/sourcegraph/sourcegraph/builds/283011/waterfall
- N=10:
https://buildkite.com/sourcegraph/sourcegraph/builds/283013/waterfall

---

From logs of some other run that I don't have the link to anymore, we
can see that some tests take up to 50s so a timeout of 60s (instead of
the default 30s) for CI should be a good new ceiling.

```
Slow test file: [chromium] › src/routes/[...repo=reporev]/(validrev)/(code)/-/blob/[...path]/page.spec.ts (48.9s)
--
  | Slow test file: [chromium] › src/routes/[...repo=reporev]/(validrev)/(code)/page.spec.ts (45.0s)
  | Slow test file: [chromium] › src/routes/search/page.spec.ts (40.6s)
  | Slow test file: [chromium] › src/routes/[...repo=reporev]/(validrev)/(code)/-/tree/[...path]/page.spec.ts (31.7s)
  | Slow test file: [chromium] › src/routes/layout.spec.ts (31.5s)

```

## Test plan

CI

## Changelog

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