[url_launcher_android] Fix unawaited_futures lint errors (#4086)

Fixes `unawaited_futures` lint errors from
https://github.com/flutter/packages/pull/4045.

This only updates the tests, so no version bump.

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to the [pub versioning philosophy], or this PR is [exempt from version
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[following repository CHANGELOG style].
- [ ] I updated/added relevant documentation (doc comments with `///`).
- [ ] I added new tests to check the change I am making, or this PR is
[test-exempt].
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packages/url_launcher/url_launcher_android/test/url_launcher_android_test.dart

@@ -86,7 +86,7 @@ void main() {
 
     test('passes through no-activity exception', () async {
       final UrlLauncherAndroid launcher = UrlLauncherAndroid(api: api);
-      expectLater(
+      await expectLater(
           launcher.launch(
             'noactivity://',
             useSafariVC: false,
@@ -101,7 +101,7 @@ void main() {
 
     test('throws if there is no handling activity', () async {
       final UrlLauncherAndroid launcher = UrlLauncherAndroid(api: api);
-      expectLater(
+      await expectLater(
           launcher.launch(
             'unknown://scheme',
             useSafariVC: false,
@@ -167,7 +167,7 @@ void main() {
 
     test('passes through no-activity exception', () async {
       final UrlLauncherAndroid launcher = UrlLauncherAndroid(api: api);
-      expectLater(
+      await expectLater(
           launcher.launch(
             'noactivity://scheme',
             useSafariVC: false,
@@ -182,7 +182,7 @@ void main() {
 
     test('throws if there is no handling activity', () async {
       final UrlLauncherAndroid launcher = UrlLauncherAndroid(api: api);
-      expectLater(
+      await expectLater(
           launcher.launch(
             'unknown://scheme',
             useSafariVC: false,