Broken sync request handling

[soxofaan]

New feature in openeo_driver was just added in Open-EO/openeo-python-driver#246 : it calls backend_implementation.processing.validate on sync request handling.

This causes failing tests in aggregator: tests.test_views.TestProcessing.test_result_backend_by_process detect additional error logging because now each sync processing request in aggregator forcibly triggers a /validation requests, which is not mocked in these tests

[soxofaan]

will start with quick fix to pin down the openeo_driver dependency to get tests working again

[soxofaan]

tests are passing again with pin openeo_driver>=0.75.0.dev<0.80.0.dev

[soxofaan]

under Open-EO/openeo-python-driver#248 we're going to revise the validation-on-sync-processing, which was reverted in openeo_driver 0.81.0, so we can remove that upper constraint again

[soxofaan]

Additional work (if any) depends on Open-EO/openeo-python-driver#248 but going to close this one for now