DEV: Bump Capybara.default_max_wait_time to 20 on CI (#32143)

There are flaky system tests that have been exhausting the 10 seconds
default max wait time which we have set previously on CI. However, I
have yet to be able to figure out why and lack the tools to be able to
figure out why. The hope here is that the upcoming playwright driver
will provide us with better tooling to debug such problems.

I've attempted to use `Capybara::Session#using_wait_time` by there is
some race condition going on where the session's default max wait time
is sometimes not set properly. I can't figure out why and have spent too
much time trying to figure out why. Instead, I will just bump up the
`default_max_wait_time` to `20`. This may the build take longer when
there are test failures but it is a trade-off we will make right now.

.github/workflows/tests.yml

@@ -38,7 +38,7 @@ jobs:
       PGUSER: discourse
       PGPASSWORD: discourse
       USES_PARALLEL_DATABASES: ${{ matrix.build_type == 'backend' || matrix.build_type == 'system' }}
-      CAPYBARA_DEFAULT_MAX_WAIT_TIME: 10
+      CAPYBARA_DEFAULT_MAX_WAIT_TIME: 20
       MINIO_RUNNER_LOG_LEVEL: DEBUG
       DISCOURSE_TURBO_RSPEC_RETRY_AND_LOG_FLAKY_TESTS: ${{ (matrix.build_type == 'system' || matrix.build_type == 'backend') && '1' }}
       CHEAP_SOURCE_MAPS: "1"