Fixes #3301. Fix SearchEngineManagerTest test.

[dector]

Issue #3301

Removed useless launch {}.join() construction in test.

I think this test was failing sometimes because we are using coroutine context from runBlockingTest with TestCoroutineDispatcher inside. But joining to job explicitly scheduled to Dispatchers.Default.

Complexity

Trivial (★☆☆)

Pull Request checklist

• Quality: This PR builds and passes detekt/ktlint checks (A pre-push hook is recommended)
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry or does not need one
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features

[jhugman]

Code looks good. This helps us a lot, thank you.

[jonalmeida]

I'm going to run this a couple of times to see if we get any intermittent failures in CI. When I originally debugged this, it wasn't as easy to repro this locally.

[dector]

@jonalmeida To reproduce this one can use something like:

launch(Dispatchers.Default) { Thread.sleep(1000) }.join()

SearchEngineManager is totally ok because we are passing (test) coroutine context to it. Using another thread (from Default dispatcher) messes test.

There are few issues in Kotlin coroutines repository for it and fix isn't merged yet.

[codecov]

Codecov Report

Merging #3309 into master will decrease coverage by 0.62%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #3309      +/-   ##
============================================
- Coverage     81.76%   81.14%   -0.63%     
+ Complexity     3275     3069     -206     
============================================
  Files           425      405      -20     
  Lines         14278    13574     -704     
  Branches       2044     1894     -150     
============================================
- Hits          11674    11014     -660     
- Misses         1765     1803      +38     
+ Partials        839      757      -82

Impacted Files	Coverage Δ	Complexity Δ
...ts/service/glean/scheduler/MetricsPingScheduler.kt	88.57% <0%> (-10%)	22% <0%> (ø)
...components/browser/session/action/BrowserAction.kt
.../browser/engine/system/matcher/ReversibleString.kt
.../components/browser/session/ext/StoreExtensions.kt
...nents/browser/engine/system/SystemEngineSession.kt
...ngine/system/permission/SystemPermissionRequest.kt
...onents/browser/engine/system/matcher/UrlMatcher.kt
.../components/browser/engine/system/NestedWebView.kt
...omponents/feature/session/bundling/ext/Snapshot.kt
...s/feature/session/bundling/SessionBundleStorage.kt
... and 27 more

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