[ML] New test fails on CI

[przemekwitek]

Recently introduced test ("Test get stats for started datafeed contains timing stats" introduced in #43045 fails on CI with broken assertion:

java.lang.AssertionError: Failure at [ml/get_datafeed_stats:198]: datafeeds.0.timing_stats.search_count didn't match expected value:
datafeeds.0.timing_stats.search_count: expected [1] but was [0]

CI details: https://groups.google.com/a/elastic.co/forum/?utm_medium=email&utm_source=footer#!msg/build-elasticsearch/tSXaX9zxqug/jWepkleFAgAJ

[elasticmachine]

Pinging @elastic/ml-core

[przemekwitek]

One hypothesis is that the test fails because it stops the datafeed soon after starting it and the datafeed may not be able to perform search.

I'll relax the assertion for now to make the test pass and then fix the test itself.

[przemekwitek]

The fix is now merged in.
Moreover, we agreed to keep this yml test only verify timing_stats existence, not the actual values. The actual values are verified in java tests.