Tests can fail when running in paralllel

[equinor-ruaj]

A recent change in the aggregation service does not allow starting a bulk aggregation job if there already exists a job on a given caseUuid + iteration combination.
Check added in this PR: https://github.com/equinor/sumo-fmu-aggregation-service/pull/288/files#diff-348e061a43670d82a0962ab0417486aa253a20533739cad241348169f0bc2ca1R125-R129

Multiple tests in .github/workflows start bulk aggregation, often using the same case and iteration.
Some of these tests may fail if a parallel test started a bulk aggregation right before it.

Possible fixes:

• Ensure the tests use separate case + iteration combinations
• Or run the tests in serial
• Or if error is that a batch job already exists, wait