Simplify ensemble evaluator shutdown timeout

[JHolba]

The timeout task was not always awaited. F.ex. if an exception was raised. This could cause issues with tests.

Approach
Replaced the task with the built-in timeout function of asyncio.wait

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'pytest tests/ert/unit_tests -n logical -m "not integration_test"')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Create Backport PR to latest release

[xjules]

Now this one fails:
FAILED tests/ert/ui_tests/cli/test_cli.py::test_that_connection_errors_do_not_effect_final_result - Failed: Timeout >360.0s

[xjules]

Good one! 🚀