Consider not importing `create_observation_dataframes` from `ert` in our tests

[GibranAlfa]

Currently we import create_observation_dataframes in our tests, but ert just recently made that method private, so we should consider if we need to import it in our tests. For now, we can keep importing create_observation_dataframes to avoid changing things, and discuss the way forward later.

Relevant change in ert:
equinor/ert@7606613#diff-51c680229ac06ac420b90d8ae0e7567679b186f2a1e470a490e42a0cd98b0911

Second arg in create_observation_dataframes() is removed:
equinor/ert@339bb9d

Import changes in our tests:

fmu-dataio/tests/test_ert_integration/test_wf_create_case_metadata.py

Lines 20 to 22 in 43b8aca

	from ert.config._create_observation_dataframes import (
	create_observation_dataframes, # TODO: consider removing this private import
	)

fmu-dataio/tests/test_units/test_workflows/test_case_observations.py

Lines 22 to 24 in 43b8aca

	from ert.config._create_observation_dataframes import (
	create_observation_dataframes, # TODO: consider removing this private import
	)

We should undo installing latest ert in CI introduced by this PR #1788 and this PR https://github.com/equinor/rms-sys/pull/916