Enable tests failing due to java-joda warnings

[pgomulka]

Tests were failing in mixed cluster after more broad warnings were
introduced in 6.x These tests were using yyyy-MM-dd pattern which
is now warning about the change of y to u. However, using predefined pattern
strict_date which uses the same format prevents the warning from being
generate and allow smooth upgrade/work in mixed cluster.
relates #42679

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[elasticmachine]

Pinging @elastic/es-core-infra

[rjernst]

This looks good, but in the future I don't think we need a separate PR for each branch. If a PR doesn't apply to master (ie is not something that could go through master), then it can target 7.x and be backported appropriately from there.

[pgomulka]

@rjernst you are right, apologies. I aimed to create a PR for 7.x and backport to 7.2 and 7.1 but forgot about the appropriate labels